diff --git a/CONTRIBUTING-mods.md b/CONTRIBUTING-mods.md
index 40147fae..3030138f 100644
--- a/CONTRIBUTING-mods.md
+++ b/CONTRIBUTING-mods.md
@@ -173,7 +173,7 @@ before the key existed changes behavior; list both generations or say `"all"`
 when you mean everywhere.
 
 `docs/mod-api-gen2-compat.md` is the compatibility matrix: what works on Gold
-and Silver today (40 of the 46 registries, 40 event and 43 hook names shared with Gen 1,
+and Silver today (40 of the 46 registries, 40 event and 44 hook names shared with Gen 1,
 and 24 Gen 2-only ones), which registries have no Gen 2 home and drop their
 writes with a report, and which hooks and events are still to come.
 `docs/preparing-your-mod-for-gen2.md` is the step-by-step migration guide for a
diff --git a/docs/mod-api-gen2-compat.md b/docs/mod-api-gen2-compat.md
index 0e7e7ffd..896b9187 100644
--- a/docs/mod-api-gen2-compat.md
+++ b/docs/mod-api-gen2-compat.md
@@ -24,7 +24,7 @@ The short version, for an author deciding what to write:
   merged.** The write is taken, dropped, and named once per mod in the same
   error feed the mod manager shows -- in both directions, so a Red boot writing
   to `decorations` is told exactly as a Gold boot writing to `map_scripts` is.
-- **40 event names and 43 hook names have a call site in both generations**, so
+- **40 event names and 44 hook names have a call site in both generations**, so
   one subscription serves both games. `tests/engine/gate_gen2_mod_api.lua`
   reads those names back out of the source and fails if a site is renamed or
   deleted on either side, and fails again if a new shared site appears without
@@ -539,7 +539,8 @@ gains a field instead of the name gaining a prefix.
   `battle.damage_dealt`, `battle.fainted`, `battle.status_inflicted`,
   `battle.battler_switched`, `battle.ball_thrown`, `battle.exp_gained`,
   `pokemon.level_up`, `pokemon.move_learned`; hooks `battle.damage`,
-  `battle.crit`, `battle.accuracy`, `battle.turn_order`,
+  `battle.crit`, `battle.accuracy`, `battle.charge_required`,
+  `battle.turn_order`,
   `battle.enemy_action`, `battle.run`, `battle.exp_award`, `exp.gain`,
   `catch.rate`, `trainer.party`, `battle.overlay`, `battle.low_health_alarm`,
   `battle.catch_exp`, `battle.bottom_ui_visible`,
diff --git a/docs/modding.md b/docs/modding.md
index 4016e1f1..7c724404 100644
--- a/docs/modding.md
+++ b/docs/modding.md
@@ -122,21 +122,40 @@ Each object requires a stable `id`, a display `name`, a destination `file`
 digests. `format` is either `"raw"` (the default) or `"n64"`. An optional
 `description` gives players dump or region guidance in the import panel.
 `size` declares the exact canonical byte length; `max_size` declares a smaller
-per-import ceiling when an exact size is not appropriate. Every import also
-has an engine-enforced 128 MiB ceiling and is rejected before hashing when its
-filesystem reports an invalid size.
+per-import ceiling when an exact size is not appropriate. The engine hard limit
+is 2 GiB. Imports above 128 MiB receive an explicit free-space confirmation and
+use the launcher's streaming large-file path rather than being materialized as
+one Lua string.
 
 For `"n64"`, the launcher recognizes `.z64`, `.v64`, and `.n64` byte orders,
 strips a recognized 512-byte copier header, converts the bytes to canonical
 big-endian `.z64` order, and then checks MD5. The canonical bytes are written
 to `mods/<mod-id>/baseroms/<file>`. Each selection is a private grant to that
 mod: the launcher never scans or copies another mod's imported files merely
-because its manifest names the same digest. Mods read the result with their existing scoped `mod:read` API, for
-example `mod:read("baseroms/stadium2.z64")`; no host path or new filesystem
+because its manifest names the same digest. Small sources can still be read
+with the existing scoped `mod:read` API, for example
+`mod:read("baseroms/stadium2.z64")`. For large sources, prefer the bounded
+`mod.imports` facade described below; no host path or new general filesystem
 permission is exposed. Missing `required_imports` block the mod before its
 entry chunk runs; missing `optional_imports` remain visible in the same
 launcher panel but do not block loading.
 
+#### Bounded access to validated imports
+
+A loaded mod can address only ids declared by its own `required_imports` or
+`optional_imports` arrays:
+
+```lua
+local info, err = mod.imports:info("stadium2")
+local header, err = mod.imports:read("stadium2", 0, 4096)
+```
+
+`read` uses zero-based offsets and is capped at 8 MiB per call. The engine
+rechecks the stored import before exposing it, seeks into the engine-owned
+copy, and never gives the mod a host path or file handle. This is intended for
+large source formats whose table/index can be parsed with small reads before
+selectively reading the payloads a transform actually needs.
+
 MD5 here identifies a known dump because ROM databases commonly publish it;
 it is not a security or authenticity guarantee. Do not paste the SHA-1 used by
 Gen1Recomp's own game-ROM importer into an import's `md5` field. Mod archives
@@ -441,6 +460,28 @@ default** (1x front, 2x back).
   ball-to-pic grow multiplies your scale through each stage, so a rescaled
   mon still grows into place from the ball, grounded the whole way.
 
+## Installation-scoped generated cache
+
+Generated data derived from a validated user source often belongs to the mod
+installation rather than to one Pokémon save. `mod.cache` is that namespace:
+
+```lua
+local ok, err = mod.cache:write("extract/v1/arena.bin", encodedArena)
+local bytes, err = mod.cache:read("extract/v1/arena.bin")
+local info = mod.cache:info("extract/v1/arena.bin")
+mod.cache:delete("extract/v1/arena.bin")
+```
+
+The physical root is engine-owned (`mod_cache/<mod-id>/`) and never exposed to
+the mod. Keys are safe relative paths and a single write is capped at 64 MiB.
+The cache does not rewind with checkpoints and is not scoped to game version,
+slot, or playthrough. The mod owns its generated format, fingerprints, rebuild
+policy, and completion marker; the engine treats the bytes as opaque data.
+
+Use `mod.storage` instead when the data belongs to one playthrough. Use
+`mod.cache` when it is a reproducible installation artifact that can be rebuilt
+from a declared user source.
+
 ## Durable tool storage and runtime checkpoints
 
 `mod.save` remains the right place for state that should travel with the next
@@ -633,6 +674,17 @@ the selected indices. Mods remain responsible for selection policy and should
 use only public `mod.ui`, hook, and save APIs. See RFC 0010 for the exact
 contract and compatibility guarantees.
 
+Both battle engines expose the guarded `battle.charge_required` hook when a
+charge-capable move is selected for its initial turn and the active ruleset
+would otherwise charge it. The wrapper receives `(next, ctx)`, where `ctx` is
+`{ battle, user, target, move, charge = true, isCalled }`. Return `false` to
+skip only that initial charge and continue through the ordinary move pipeline;
+call `next(ctx)` to keep it. The hook does not run for the release turn or when
+the active ruleset already skips charging (for example, Gold Solarbeam in
+sun). PP use, accuracy, damage, animation, and secondary effects remain owned
+by the engine. With no subscriber, the vanilla decision runs without building
+the hook context.
+
 ## Developer console
 
 Boot with developer mode on to unlock the in-game console and hot-reload
diff --git a/docs/rfcs/0008-streamed-mod-imports-and-install-cache.md b/docs/rfcs/0008-streamed-mod-imports-and-install-cache.md
new file mode 100644
index 00000000..22240416
--- /dev/null
+++ b/docs/rfcs/0008-streamed-mod-imports-and-install-cache.md
@@ -0,0 +1,141 @@
+# RFC 0008 — Streamed mod imports and installation-scoped generated cache
+
+## Motivation
+
+`required_imports`/`optional_imports` can now describe files up to 2 GiB, but
+the existing launcher and public mod API still assume imported bytes are small:
+
+* the Windows desktop picker stages a selected required import through a fixed
+  `%TEMP%/pokeport_required_import.bin` path before validation;
+* the fallback import path materializes the selected file as one Lua string;
+* after validation a mod can only use `mod:read("baseroms/...")`, which also
+  materializes the whole file;
+* `mod.storage` is intentionally scoped to one Pokémon playthrough, so it is
+  not an appropriate home for a one-time generated asset cache shared by every
+  save using the same installed mod.
+
+This makes optical-disc-sized user sources impractical even though the manifest
+schema already accepts them. A failed temporary staging copy can also turn a
+valid large source into a smaller temporary file and produce a misleading
+"wrong file size" rejection.
+
+A mod should be able to consume its own already-validated source incrementally
+and compile derived runtime data once, without receiving a host path or general
+filesystem access.
+
+## Decision being extended
+
+This extends the same legal/sandbox direction as **D11 asset transforms**
+(`src/mods/AssetTransform.lua`): mods distribute recipes and derive bytes from
+user-owned sources rather than shipping ROM-derived data. It also follows the
+**D14 parity-gate** contract referenced by `tests/harness.lua` and
+`tests/engine/gate_meta_coverage.lua` (the `21-testing-and-ci` plan): additive
+extension points ship public-API coverage, no-mod parity coverage, and docs in
+the same change.
+
+The historical D11 plan document is referenced by source comments but is not
+present in the current repository tree; this RFC is the checked-in design
+record for the new surface.
+
+## Exact API delta
+
+No manifest field changes. Existing `required_imports` and `optional_imports`
+remain the declaration/validation authority.
+
+Two additive facades are added to the `mod` object.
+
+### `mod.imports`
+
+```lua
+local info, err = mod.imports:info("source_id")
+local bytes, err = mod.imports:read("source_id", offset, length)
+```
+
+* `source_id` must name an import declared by the calling mod.
+* the import is rechecked through `RequiredImports.validateStored` before it is
+  exposed, so missing, replaced, or invalid optional imports are not readable;
+* `offset` and `length` are zero-based byte coordinates;
+* one read is capped at 8 MiB;
+* no host path or file handle is returned;
+* production reads seek into the engine-owned stored copy instead of reading
+  the whole source.
+
+`info()` returns declaration metadata plus stored size. It does not expose a
+host path.
+
+### `mod.cache`
+
+```lua
+mod.cache:write("extract/v1/model.bin", bytes)
+local bytes = mod.cache:read("extract/v1/model.bin")
+local info = mod.cache:info("extract/v1/model.bin")
+mod.cache:delete("extract/v1/model.bin")
+```
+
+The cache is rooted at `mod_cache/<mod-id>/`, follows the engine persistence
+backend, and is independent of game version, launcher slot, and playthrough.
+Paths are checked with `SafePath`; `..`, absolute paths, drive paths, and other
+escapes remain unavailable. A single cache write is capped at 64 MiB so large
+generated datasets are naturally split into independently replaceable files.
+
+The engine does not interpret cache bytes. Mods own generated-format versioning,
+fingerprints, transactional completion markers, and rebuild policy.
+
+## Launcher/import transport delta
+
+For large raw required imports:
+
+1. desktop pickers return the original selected path instead of staging it
+   through a fixed temporary file;
+2. the engine opens that source itself;
+3. bytes are copied directly to the existing engine-owned
+   `mods/<id>/baseroms/<file>` destination in 4 MiB chunks;
+4. MD5 is updated incrementally during the copy;
+5. the normal size/MD5 validation receipt is written only after the complete
+   destination passes validation;
+6. partial destinations are removed on short reads, write failure, size
+   mismatch, or digest mismatch.
+
+N64 imports stay on the existing canonicalization path because byte-order and
+copier-header normalization require transformation rather than a raw copy.
+
+If a validation receipt for an already-stored large raw import is missing, the
+engine rebuilds it with streaming MD5 rather than a whole-file read.
+
+## Backward compatibility / migration
+
+**Existing mods do nothing.** This is additive.
+
+* manifest v1/v2 fields are unchanged;
+* `mod:read`, `mod.storage`, registries, events, hooks, and legacy compatibility
+  retain their existing behavior;
+* small required imports retain the existing in-memory validation path;
+* N64 imports retain canonicalization and existing accepted byte orders;
+* a mod that never touches `mod.imports` or `mod.cache` creates no new cache
+  files and observes no new behavior.
+
+The mod API integer is not bumped because no existing member changes meaning or
+shape.
+
+## Security and legal posture
+
+The launcher remains the authority that validates user-supplied bytes. The new
+facade narrows access rather than widening it: a mod can read only ids declared
+in its own manifest, only after validation, and only in bounded ranges. It does
+not receive host paths, `io`, or a raw filesystem handle.
+
+`mod.cache` is writable only beneath the calling mod's generated-cache root.
+Nothing in this RFC permits packaged ROM-derived bytes; `modkit lint/pack`
+continue to enforce the existing legal posture.
+
+## Parity guarantee
+
+The change ships with:
+
+* a no-mod/API-v1 parity test proving an empty load and an existing v1-style
+  `mod:read` load do not create cache data or change the old surface;
+* a public mod-API test that reaches `mod.imports` and `mod.cache` through a
+  real `Loader` load, including bounded reads, undeclared/missing imports,
+  cache isolation, and traversal rejection;
+* incremental MD5 vectors and a large-import streaming regression test;
+* the existing engine suite, required-import suite, and mod lint gates.
diff --git a/docs/rfcs/0011-battle-charge-required.md b/docs/rfcs/0011-battle-charge-required.md
new file mode 100644
index 00000000..310bec00
--- /dev/null
+++ b/docs/rfcs/0011-battle-charge-required.md
@@ -0,0 +1,92 @@
+# RFC 0011: Charge-required battle hook
+
+## Status
+
+Proposed.
+
+## Motivation
+
+A battle-mechanics mod can change damage through `battle.damage` and register
+move effects, but it cannot conditionally skip the first turn of an existing
+charge move. In Gen 1, the engine decides and stores the charge continuation
+before any public effect callback can run. Reaching into `user.charging`,
+`user.chargeReady`, or generation-specific volatile state is private,
+checkpoint-fragile, and would require a mod to duplicate move-pipeline policy.
+
+Weather is the immediate example: a portable sun rule needs Solarbeam to
+resolve on selection while leaving Fly, Dig, PP use, hit resolution, animation,
+and secondary effects to the engine. The capability is generic and useful to
+other ruleset and move-mechanics mods.
+
+## Decision and plan extended
+
+This implements **D-AT-002: charge-stage policy remains mod authority through a
+generic guarded engine decision seam**. The consuming design is tracked in the
+Adaptive Trainers implementation plan,
+[`docs/superpowers/plans/2026-08-14-adaptive-trainers.md`](https://github.com/MaxTomahawk/gen1recomp-adaptive-trainers/blob/main/docs/superpowers/plans/2026-08-14-adaptive-trainers.md),
+Task 8. The delta follows the additive, guarded hook convention documented by
+Route B in `CONTRIBUTING-mods.md`; it contains no weather, move-id, trainer, or
+Adaptive Trainers policy.
+
+## Exact API delta
+
+Both the Gen 1 and Gen 2 battle engines add this guarded hook:
+
+```lua
+mod.hooks:wrap("battle.charge_required", function(next, ctx)
+  -- ctx = {
+  --   battle = live battle controller,
+  --   user = attacking battler,
+  --   target = defending battler,
+  --   move = merged move record,
+  --   charge = true,
+  --   isCalled = false,
+  -- }
+  if should_resolve_now(ctx) then return false end
+  return next(ctx)
+end)
+```
+
+The call site is the initial-use charge decision, after announcement and PP
+handling but before charge state, invulnerability, charge animation, or charge
+text is created. It runs only when the active engine rules would otherwise
+require a charge. It does not run on the release turn. Returning exactly
+`false` skips that initial charge and continues through the engine-owned move
+pipeline. Any other downstream return preserves the charge. `isCalled` is true
+when Metronome or Mirror Move selected the move.
+
+Gold keeps its native sun decision first, so Solarbeam in native sun already
+requires no charge and does not invoke the hook. Gen 1 link battles use the
+shared Gen 1 move pipeline and therefore receive the same seam; normal link
+mod-compatibility rules continue to govern deterministic peers.
+
+The hot path first calls `Runtime.wantsHook("battle.charge_required")`. With no
+subscriber, no hook payload table is allocated and the existing branch runs
+unchanged.
+
+## Migration and compatibility
+
+Existing mods change nothing. The hook name and payload are additive. With no
+wrapper installed, Red, Blue, Yellow, Gold, and Silver retain their previous
+charge state, PP use, text, animation, accuracy, damage, and native weather
+behavior. Existing charge-move data and effect records require no migration.
+
+A mod adopting the seam should call `next(ctx)` unless it deliberately wants to
+skip this charge. It should not mutate private charge fields or re-run the move.
+
+## Verification
+
+- `tests/engine/battle_charge_required.lua` exercises the real Gen 1 and Gen 2
+  engines through a sandboxed public mod, including false-to-skip, next-to-keep,
+  release-turn behavior, called-move PP semantics, shared payload shape, and
+  native Gold sun behavior.
+- The same test proves no-mod charge/release parity and replaces
+  `Runtime.call` with a sentinel behind a false `Runtime.wantsHook` guard.
+- `tests/engine/gate_hooks.lua` discovers the new catalog name and proves empty
+  chains preserve vanilla values and allocation behavior.
+- `tests/engine/gate_gen2_mod_api.lua` requires a guarded site in both
+  generations and keeps the compatibility reference list complete.
+
+## Deprecation etiquette
+
+Nothing is removed, renamed, superseded, or deprecated.
diff --git a/src/battle/BattleState.lua b/src/battle/BattleState.lua
index 4a61ef0a..3a005361 100644
--- a/src/battle/BattleState.lua
+++ b/src/battle/BattleState.lua
@@ -3980,7 +3980,17 @@ function BattleState:performMove(user, target, moveInst, isCalled)
   -- record (chargeText) and the invulnerability from semiInvulnerable,
   -- falling back to the id tables (Fly AND Dig go semi-invulnerable:
   -- ChargeEffect sets INVULNERABLE for both)
-  if record and record.charge and not releasing then
+  local chargeRequired = record and record.charge ~= nil and not releasing
+  if chargeRequired and Runtime.wantsHook("battle.charge_required") then
+    local required = Runtime.call("battle.charge_required", function(c)
+      return c.charge
+    end, {
+      battle = self, user = user, target = target, move = move,
+      charge = true, isCalled = isCalled or false,
+    })
+    chargeRequired = required ~= false
+  end
+  if chargeRequired then
     self:cancelMoveAnim()
     user.charging = moveInst
     user.chargeReady = true
diff --git a/src/battle/gen2/Battle.lua b/src/battle/gen2/Battle.lua
index 06d57035..9346f9dd 100644
--- a/src/battle/gen2/Battle.lua
+++ b/src/battle/gen2/Battle.lua
@@ -1494,6 +1494,15 @@ function Battle:useMove(attacker, defender, moveId)
   if def.effect == "EFFECT_SOLARBEAM" and self.weather == "sun" then
     charge = nil
   end
+  if charge and not charging and Runtime.wantsHook("battle.charge_required") then
+    local required = Runtime.call("battle.charge_required", function(c)
+      return c.charge
+    end, {
+      battle = self, user = attacker, target = defender, move = def,
+      charge = true, isCalled = (self.copyDepth or 0) > 0,
+    })
+    if required == false then charge = nil end
+  end
   if charge and not charging then
     state.chargeMove = moveId
     state.vanished = charge.vanish or nil
diff --git a/src/import/CacheFs.lua b/src/import/CacheFs.lua
index a3bfd889..00ef8e99 100644
--- a/src/import/CacheFs.lua
+++ b/src/import/CacheFs.lua
@@ -287,6 +287,43 @@ function CacheFs.write(rel, data)
   return love.filesystem.write(rel, data)
 end
 
+-- Open a cache-relative file for streaming replacement. The returned handle
+-- has write(bytes) and close() methods and follows the same portable/save-dir
+-- routing as CacheFs.write without forcing the caller to hold the whole file
+-- in one Lua string.
+function CacheFs.openWrite(rel)
+  rel = withPrefix(rel)
+  local root = CacheFs.root()
+  if root then
+    ensureParents(root, rel)
+    local f, err = io.open(realPath(root, rel), "wb")
+    if not f then return nil, err end
+    return {
+      write = function(_, data)
+        local ok, writeErr = f:write(data)
+        if not ok then return nil, writeErr end
+        return true
+      end,
+      close = function() f:close() end,
+    }
+  end
+  if not (love and love.filesystem and love.filesystem.newFile) then
+    return nil, "streaming cache writes are unavailable"
+  end
+  local parent = rel:match("^(.*)/[^/]+$")
+  if parent and not love.filesystem.createDirectory(parent) then
+    local info = love.filesystem.getInfo(parent)
+    local reason = info and ("a " .. info.type .. " already exists there")
+      or "unknown reason"
+    return nil, "could not create " .. parent .. ": " .. reason
+  end
+  local file, makeErr = love.filesystem.newFile(rel)
+  if not file then return nil, makeErr or "could not create cache file" end
+  local ok, openErr = file:open("w")
+  if not ok then return nil, openErr or "could not open cache file" end
+  return file
+end
+
 -- read cache-relative `rel`; returns the bytes or nil
 function CacheFs.read(rel)
   rel = withPrefix(rel)
diff --git a/src/import/RomImporter.lua b/src/import/RomImporter.lua
index 63221a14..f1dff9c9 100644
--- a/src/import/RomImporter.lua
+++ b/src/import/RomImporter.lua
@@ -388,6 +388,142 @@ local function externalFileSize(path)
   return size
 end
 
+local function openImportSource(path)
+  -- Desktop picker paths live outside LÖVE's virtual filesystem. Prefer the
+  -- native file handle so a 1.46 GiB disc is never copied to a temp file or
+  -- read into one Lua string before validation.
+  local native = io.open(path, "rb")
+  if native then
+    local size, sizeErr = native:seek("end")
+    if size == nil or size == false then
+      native:close()
+      return nil, sizeErr or "could not determine source file size"
+    end
+    local reset, resetErr = native:seek("set", 0)
+    if reset == nil or reset == false then
+      native:close()
+      return nil, resetErr or "could not rewind source file"
+    end
+    return {
+      size = size,
+      read = function(_, n) return native:read(n) end,
+      close = function() native:close() end,
+    }
+  end
+  if love and love.filesystem and love.filesystem.newFile then
+    local file, makeErr = love.filesystem.newFile(path)
+    if not file then return nil, makeErr or "could not open source file" end
+    local ok, openErr = file:open("r")
+    if not ok then return nil, openErr or "could not open source file" end
+    local size = file.getSize and file:getSize() or nil
+    return {
+      size = size,
+      read = function(_, n) return file:read(n) end,
+      close = function() file:close() end,
+    }
+  end
+  return nil, "streaming source access is unavailable"
+end
+local function streamRequiredImport(manifest, importId, source)
+  local RequiredImports = require("src.mods.RequiredImports")
+  local spec = RequiredImports.spec(manifest, importId)
+  if not spec then return nil, "Import declaration was not found." end
+  if spec.format == "n64" then
+    return nil, "streaming canonicalization is unavailable for N64 imports"
+  end
+  local input, openErr = openImportSource(source)
+  if not input then return nil, openErr end
+  local sizeErr = RequiredImports.sizeError(spec, input.size, false)
+  if sizeErr then input:close(); return nil, sizeErr end
+
+  local CacheFs = require("src.import.CacheFs")
+  local destination = RequiredImports.path(manifest, spec)
+  local savedPrefix = CacheFs.prefix
+  local output
+  local inputClosed, outputClosed = false, false
+
+  local function closeInput()
+    if inputClosed then return end
+    inputClosed = true
+    pcall(function() input:close() end)
+  end
+
+  local function closeOutput()
+    if outputClosed or not output then return end
+    outputClosed = true
+    pcall(function() output:close() end)
+  end
+
+  local resultOk, resultDetail
+  CacheFs.prefix = ""
+  local ran, thrown = xpcall(function()
+    CacheFs.remove(RequiredImports.receiptPath(manifest, spec))
+    CacheFs.remove(destination)
+    local makeErr
+    output, makeErr = CacheFs.openWrite(destination)
+    if not output then
+      resultDetail = makeErr or "could not create imported file"
+      return
+    end
+
+    local MD5 = require("src.mods.StreamMD5")
+    local md5 = MD5.new()
+    local total, chunkBytes = 0, 4 * 1024 * 1024
+    while true do
+      local chunk = input:read(chunkBytes)
+      if not chunk or #chunk == 0 then break end
+      md5:update(chunk)
+      local wrote, writeErr = output:write(chunk)
+      if wrote == false or wrote == nil then
+        resultDetail = "could not copy import: "
+.. tostring(writeErr or "write failed")
+        return
+      end
+      total = total + #chunk
+      if #chunk < chunkBytes then break end
+    end
+
+    closeInput()
+    closeOutput()
+    if input.size and total ~= input.size then
+      resultDetail = ("source read ended early (expected %d bytes, copied %d)")
+        :format(input.size, total)
+      return
+    end
+    local storedSizeErr = RequiredImports.sizeError(spec, total, true)
+    if storedSizeErr then resultDetail = storedSizeErr; return end
+    local digest = md5:final()
+
+    -- acceptStoredDigest uses the normal engine path/receipt rules, so
+    -- restore the caller's prefix before handing control to it.
+    CacheFs.prefix = savedPrefix
+    local accepted, detail = RequiredImports.acceptStoredDigest(
+      manifest, importId, digest, love.filesystem)
+    if not accepted then resultDetail = detail; return end
+    resultOk, resultDetail = true, detail
+  end, function(err)
+    if debug and debug.traceback then
+      return debug.traceback(tostring(err), 2)
+    end
+    return tostring(err)
+  end)
+
+  -- finally: resource handles and the process-global CacheFs prefix must
+  -- be restored even when a read/hash/write helper raises a Lua error.
+  closeInput()
+  closeOutput()
+  CacheFs.prefix = ""
+  if not ran or not resultOk then
+    pcall(function() CacheFs.remove(destination) end)
+  end
+  CacheFs.prefix = savedPrefix
+
+  if not ran then
+    return nil, "could not copy import: " .. tostring(thrown)
+  end
+  if not resultOk then return nil, resultDetail end
+  return true, resultDetail
+end
 local function readDroppedFile(file)
   local ok, openError = file:open("r")
   if not ok then return nil, openError end
@@ -1234,11 +1370,13 @@ local function chooseRequiredFile()
       "$d=New-Object System.Windows.Forms.OpenFileDialog;",
       "$d.Title='" .. prompt .. "';",
       "$d.Filter='All files (*.*)|*.*';",
+      -- Required imports can be multi-gigabyte optical-disc images. Do NOT
+      -- stage them through %TEMP%: that doubles free-space requirements and a
+      -- failed Copy-Item can leave a plausible-looking truncated temp file.
+      -- Stream the selected source directly into the mod-owned destination.
       "if($d.ShowDialog() -eq 'OK'){",
-      "$t=Join-Path $env:TEMP 'pokeport_required_import.bin';",
-      "Copy-Item -LiteralPath $d.FileName -Destination $t -Force;",
       "[Console]::OutputEncoding=[Text.Encoding]::UTF8;",
-      "[Console]::Write($t)}",
+      "[Console]::Write($d.FileName)}",
     })
     return commandOutput(
       'powershell -NoProfile -STA -Command "' .. script .. '"')
@@ -2078,8 +2216,13 @@ function RomImporter:_importRequiredSource(modId, importId, source, confirmed)
     return nil
   end
   local RequiredImports = require("src.mods.RequiredImports")
-  local info = love.filesystem.getInfo(source, "file")
-  local size = info and info.size or externalFileSize(source)
+  -- A desktop picker returns a host path. Ask the host file handle first;
+  -- love.filesystem.getInfo is only authoritative for virtual/save paths.
+  local size = externalFileSize(source)
+  if not size then
+    local info = love.filesystem.getInfo(source, "file")
+    size = info and info.size or nil
+  end
   local sizeErr = RequiredImports.sizeError(spec, size, false)
   if sizeErr then
     requiredImportNotice(self, modId, importId, sizeErr)
@@ -2102,6 +2245,20 @@ function RomImporter:_importRequiredSource(modId, importId, source, confirmed)
     }
     return nil
   end
+  if type(size) == "number" and size > RequiredImports.LARGE_WARN_BYTES
+      and spec.format ~= "n64" then
+    local ok, result = streamRequiredImport(manifest, importId, source)
+    if ok then
+      self.requiredImportNotice = nil
+      self.modNotice = { ok = true, text = "Imported " .. tostring(importId)
+        .. " for " .. tostring(manifest.name or manifest.id) .. "." }
+      self:_refreshMods()
+      return true
+    end
+    requiredImportNotice(self, modId, importId, result)
+    self.modNotice = nil
+    return nil
+  end
   local data = love.filesystem.read(source)
   if not data then data = readExternalPath(source) end
   if not data then
diff --git a/src/mods/ImportAccess.lua b/src/mods/ImportAccess.lua
new file mode 100644
index 00000000..11f32380
--- /dev/null
+++ b/src/mods/ImportAccess.lua
@@ -0,0 +1,174 @@
+-- Scoped access to a mod's launcher-validated required/optional imports and
+-- to installation-wide generated cache data.
+--
+-- This intentionally does not expose host paths or raw filesystem handles.
+-- Import reads are bounded and can only address ids declared by the calling
+-- mod's manifest. Cache paths are confined to mod_cache/<mod-id>/ and are not
+-- tied to a Pokémon playthrough.
+
+local RequiredImports = require("src.mods.RequiredImports")
+local SafePath = require("src.mods.SafePath")
+local SaveData = require("src.core.SaveData")
+
+local ImportAccess = {}
+
+ImportAccess.MAX_READ_BYTES = 8 * 1024 * 1024
+ImportAccess.MAX_CACHE_WRITE_BYTES = 64 * 1024 * 1024
+
+local function specMap(manifest)
+  local out = {}
+  for _, spec in ipairs(RequiredImports.specs(manifest)) do out[spec.id] = spec end
+  return out
+end
+
+local function parentOf(path)
+  return path:match("^(.*)/[^/]+$")
+end
+
+local function copyInfo(info)
+  if not info then return nil end
+  return { type = info.type, size = info.size, modtime = info.modtime }
+end
+
+local function fsReadRange(fs, path, offset, length)
+  if fs and type(fs.readRange) == "function" then
+    return fs.readRange(path, offset, length)
+  end
+  local newFile = fs and fs.newFile
+  if newFile then
+    local file, makeErr = newFile(path)
+    if not file then return nil, makeErr or "could not open import" end
+    local ok, openErr = file:open("r")
+    if not ok then return nil, openErr or "could not open import" end
+    local seekOk, seekErr = file:seek(offset)
+    if seekOk == nil or seekOk == false then
+      file:close()
+      return nil, seekErr or "could not seek import"
+    end
+    local data, readErr = file:read(length)
+    file:close()
+    return data, readErr
+  end
+  -- Injectable headless filesystems may expose only read(). Production
+  -- love.filesystem has newFile(), so large imports are never materialized
+  -- into one Lua string by this fallback.
+  if fs and fs.read then
+    local data = fs.read(path)
+    if type(data) ~= "string" then return nil, "could not read import" end
+    return data:sub(offset + 1, offset + length)
+  end
+  return nil, "random-access import reads are unavailable"
+end
+
+local function validatedInfo(manifest, spec, fs)
+  local ok, detail = RequiredImports.validateStored(manifest, spec, fs)
+  if not ok then return nil, detail or "import is not validated" end
+  local path = RequiredImports.path(manifest, spec)
+  local info = fs.getInfo and fs.getInfo(path, "file") or nil
+  if not info then return nil, "import is missing" end
+  return info, detail
+end
+
+local function makeCache(modId, fs)
+  local root = "mod_cache/" .. modId
+  local function pathFor(rel, what)
+    rel = SafePath.require(rel, what or "mod.cache path")
+    return root .. "/" .. rel
+  end
+  local cache = {}
+
+  function cache:write(rel, bytes)
+    if type(bytes) ~= "string" then
+      return nil, "mod.cache:write expects a byte string"
+    end
+    if #bytes > ImportAccess.MAX_CACHE_WRITE_BYTES then
+      return nil, "mod.cache:write payload exceeds 64 MiB; split generated data into smaller files"
+    end
+    local path = pathFor(rel, "mod.cache:write")
+    local parent = parentOf(path)
+    if parent and fs.createDirectory then
+      local ok = fs.createDirectory(parent)
+      if ok == false then return nil, "could not create cache directory" end
+    end
+    if not fs.write then return nil, "cache writes are unavailable" end
+    return fs.write(path, bytes)
+  end
+
+  function cache:read(rel)
+    local path = pathFor(rel, "mod.cache:read")
+    if not fs.read then return nil, "cache reads are unavailable" end
+    return fs.read(path)
+  end
+
+  function cache:info(rel)
+    local path = pathFor(rel, "mod.cache:info")
+    if not fs.getInfo then return nil end
+    return copyInfo(fs.getInfo(path))
+  end
+
+  function cache:exists(rel)
+    local info = self:info(rel)
+    return info ~= nil and info.type == "file"
+  end
+
+
+  function cache:delete(rel)
+    local path = pathFor(rel, "mod.cache:delete")
+    if not fs.remove then return nil, "cache deletion is unavailable" end
+    return fs.remove(path)
+  end
+
+  return cache
+end
+
+function ImportAccess.new(manifest, fs)
+  local specs = specMap(manifest)
+  local cacheFs = SaveData.persistenceFs(fs) or fs
+  local imports = {}
+
+  function imports:info(id)
+    local spec = specs[id]
+    if not spec then return nil, "undeclared import: " .. tostring(id) end
+    local info, digestOrErr = validatedInfo(manifest, spec, fs)
+    if not info then return nil, digestOrErr end
+    return {
+      id = spec.id,
+      name = spec.name,
+      file = spec.file,
+      size = info.size,
+      md5 = digestOrErr,
+      required = spec.required ~= false,
+    }
+  end
+
+  function imports:read(id, offset, length)
+    local spec = specs[id]
+    if not spec then return nil, "undeclared import: " .. tostring(id) end
+    offset, length = tonumber(offset), tonumber(length)
+    if not offset or offset < 0 or offset % 1 ~= 0 then
+      return nil, "offset must be a non-negative integer"
+    end
+    if not length or length < 0 or length % 1 ~= 0 then
+      return nil, "length must be a non-negative integer"
+    end
+    if length > ImportAccess.MAX_READ_BYTES then
+      return nil, "single import read exceeds 8 MiB"
+    end
+
+    local info, err = validatedInfo(manifest, spec, fs)
+    if not info then return nil, err end
+    local size = tonumber(info.size) or tonumber(spec.size)
+    if size and offset + length > size then return nil, "import read is out of bounds" end
+    if length == 0 then return "" end
+
+    local path = RequiredImports.path(manifest, spec)
+    local data, readErr = fsReadRange(fs, path, offset, length)
+    if not data then return nil, readErr end
+    if #data ~= length then return nil, "short import read" end
+    return data
+  end
+
+  return imports, makeCache(manifest.id, cacheFs)
+end
+
+return ImportAccess
diff --git a/src/mods/Loader.lua b/src/mods/Loader.lua
index 8ec4767d..ddfc3f12 100644
--- a/src/mods/Loader.lua
+++ b/src/mods/Loader.lua
@@ -962,6 +962,8 @@ function Loader:_api(mod)
   local Storage = engineRequire("src.mods.Storage")
   local storage = Storage and Storage.new(modId, loader.fs)
   local Checkpoint = engineRequire("src.core.Checkpoint")
+  local ImportAccess = engineRequire("src.mods.ImportAccess")
+  local importApi, installCache = ImportAccess.new(mod.manifest, loader.fs)
   local api = {
     id = modId,
     version = mod.manifest.version,
@@ -1161,6 +1163,12 @@ function Loader:_api(mod)
     -- checkpoint. The
     -- engine binds version/playthrough/mod scope and portable persistence;
     -- callers never receive paths or a raw filesystem handle.
+    -- Read-only bounded access to this mod's manifest-declared, launcher-validated
+    -- imports. No host path is exposed; large sources are read in bounded ranges.
+    imports = importApi,
+    -- Installation-scoped generated data, independent from Pokémon save slots.
+    -- This is where ROM-derived caches belong; mod.storage remains playthrough-scoped.
+    cache = installCache,
     storage = {
       context = function(_, game) return storage:context(game) end,
       selected = function(_, game) return storage:selected(game) end,
diff --git a/src/mods/RequiredImports.lua b/src/mods/RequiredImports.lua
index 806e916e..cfdb9b42 100644
--- a/src/mods/RequiredImports.lua
+++ b/src/mods/RequiredImports.lua
@@ -120,6 +120,36 @@ local function accepts(spec, digest)
   return false
 end
 
+local function specById(manifest, importId)
+  for _, candidate in ipairs(allSpecs(manifest)) do
+    if candidate.id == importId then return candidate end
+  end
+  return nil
+end
+
+RequiredImports.spec = specById
+
+local function streamDigest(fs, path, chunkBytes)
+  if not (fs and fs.newFile) then return nil, "streaming file access is unavailable" end
+  local file, makeErr = fs.newFile(path)
+  if not file then return nil, makeErr or "could not open stored import" end
+  local ok, openErr = file:open("r")
+  if not ok then return nil, openErr or "could not open stored import" end
+  local MD5 = require("src.mods.StreamMD5")
+  local ctx = MD5.new()
+  chunkBytes = chunkBytes or (4 * 1024 * 1024)
+  while true do
+    local data, readErr = file:read(chunkBytes)
+    if data and #data > 0 then ctx:update(data) end
+    if not data or #data < chunkBytes then
+      if readErr then file:close(); return nil, readErr end
+      break
+    end
+  end
+  file:close()
+  return ctx:final()
+end
+
 function RequiredImports.path(manifest, spec)
   return manifest.path .. "/baseroms/" .. spec.file
 end
@@ -180,6 +210,47 @@ local function removeReceipt(manifest, spec, fs)
   end
 end
 
+-- Finalize a caller-streamed import after the destination bytes have already
+-- been copied into the engine-owned baseroms path. This keeps large imports
+-- out of a single Lua string while preserving the same size/MD5 receipt rules.
+function RequiredImports.acceptStoredDigest(manifest, importId, digest, fs)
+  fs = fs or (love and love.filesystem)
+  local spec = specById(manifest, importId)
+  if not spec then return nil, "unknown required import: " .. tostring(importId) end
+  digest = tostring(digest or ""):lower()
+  if not accepts(spec, digest) then
+    return nil, ("MD5 mismatch (got %s)"):format(digest ~= "" and digest or "unavailable")
+  end
+  local path = RequiredImports.path(manifest, spec)
+  local info = fs and fs.getInfo and fs.getInfo(path, "file") or nil
+  if not info then return nil, "copied import is missing" end
+  local sizeErr = RequiredImports.sizeError(spec, info.size, true)
+  if sizeErr then return nil, sizeErr end
+  if love and fs == love.filesystem then
+    local savedPrefix = CacheFs.prefix
+    local ok, prefixErr = xpcall(function()
+      CacheFs.prefix = ""
+      CacheFs.remove(removedMarker(manifest, spec))
+      CacheFs.prefix = savedPrefix
+      -- writeReceipt has its own temporary CacheFs prefix switch. Keep it
+      -- inside this guard too so a write error cannot leak global state.
+      writeReceipt(manifest, spec, digest, info, fs)
+    end, function(err)
+      return tostring(err)
+    end)
+    CacheFs.prefix = savedPrefix
+    if not ok then
+      return nil, "could not finalize import receipt: " .. tostring(prefixErr)
+    end
+    return true, digest
+  elseif fs and fs.remove then
+    fs.remove(removedMarker(manifest, spec))
+  end
+  writeReceipt(manifest, spec, digest, info, fs)
+  return true, digest
+end
+
+
 -- Validate bytes against a declaration.  The returned data is canonicalized
 -- (notably for N64 byte order/header variants) and is what must be stored.
 function RequiredImports.validateData(spec, data, hashFn)
@@ -217,6 +288,22 @@ function RequiredImports.validateStored(manifest, spec, fs, hashFn)
   local cached = cachedDigest(manifest, spec, fs, info)
   if cached then return true, cached, true end
   removeReceipt(manifest, spec, fs)
+  -- Large raw imports (GameCube discs, future optical images, etc.) must never
+  -- be materialized into one Lua string merely because their validation
+  -- receipt was lost. Stream the MD5 directly from the installed file. N64
+  -- sources stay on the canonicalization path because byte-order/header
+  -- normalization is part of their validation contract.
+  if info.size and info.size > RequiredImports.LARGE_WARN_BYTES
+      and spec.format ~= "n64" and fs.newFile then
+    local digest, hashErr = streamDigest(fs, path)
+    if not digest then return nil, hashErr end
+    if not accepts(spec, digest) then
+      return nil, ("MD5 mismatch (got %s)"):format(digest)
+    end
+    info = fs.getInfo(path, "file") or info
+    writeReceipt(manifest, spec, digest, info, fs)
+    return true, digest, false
+  end
   if not fs.read then return nil, "file could not be read" end
   local data = fs.read(path)
   local normalized, detail = RequiredImports.validateStoredData(spec, data, hashFn)
diff --git a/src/mods/StreamMD5.lua b/src/mods/StreamMD5.lua
new file mode 100644
index 00000000..1990e8ec
--- /dev/null
+++ b/src/mods/StreamMD5.lua
@@ -0,0 +1,101 @@
+local bitlib = rawget(_G, "bit") or rawget(_G, "bit32")
+if not bitlib then error("StreamMD5 requires bit or bit32") end
+
+local band, bor, bxor, bnot = bitlib.band, bitlib.bor, bitlib.bxor, bitlib.bnot
+local lshift, rshift = bitlib.lshift, bitlib.rshift
+local rol = bitlib.rol or bitlib.lrotate
+
+local K = {
+  0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,
+  0x698098d8,0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193,0xa679438e,0x49b40821,
+  0xf61e2562,0xc040b340,0x265e5a51,0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8,
+  0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905,0xfcefa3f8,0x676f02d9,0x8d2a4c8a,
+  0xfffa3942,0x8771f681,0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60,0xbebfbc70,
+  0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05,0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,
+  0xf4292244,0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92,0xffeff47d,0x85845dd1,
+  0x6fa87e4f,0xfe2ce6e0,0xa3014314,0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391,
+}
+local S = {
+  7,12,17,22, 7,12,17,22, 7,12,17,22, 7,12,17,22,
+  5,9,14,20, 5,9,14,20, 5,9,14,20, 5,9,14,20,
+  4,11,16,23, 4,11,16,23, 4,11,16,23, 4,11,16,23,
+  6,10,15,21, 6,10,15,21, 6,10,15,21, 6,10,15,21,
+}
+
+local function add32(a,b,c,d)
+  local n = (a or 0) + (b or 0) + (c or 0) + (d or 0)
+  return band(n, 0xffffffff)
+end
+
+local function le32_from(s, i)
+  local b1,b2,b3,b4 = s:byte(i, i+3)
+  return bor(b1, lshift(b2,8), lshift(b3,16), lshift(b4,24))
+end
+
+local function le32_bytes(x)
+  return string.char(
+    band(x,0xff), band(rshift(x,8),0xff),
+    band(rshift(x,16),0xff), band(rshift(x,24),0xff))
+end
+
+local M = {}
+local StreamMD5 = {}
+StreamMD5.__index = StreamMD5
+
+function StreamMD5.new()
+  return setmetatable({
+    a=0x67452301, b=0xefcdab89, c=0x98badcfe, d=0x10325476,
+    bytes=0, buffer="", done=false,
+  }, StreamMD5)
+end
+
+function StreamMD5:_block(block)
+  for j=1,16 do M[j] = le32_from(block, (j-1)*4+1) end
+  local a,b,c,d = self.a,self.b,self.c,self.d
+  for i=0,63 do
+    local f,g
+    if i < 16 then
+      f = bor(band(b,c), band(bnot(b),d)); g=i
+    elseif i < 32 then
+      f = bor(band(d,b), band(bnot(d),c)); g=(5*i+1)%16
+    elseif i < 48 then
+      f = bxor(b,c,d); g=(3*i+5)%16
+    else
+      f = bxor(c, bor(b,bnot(d))); g=(7*i)%16
+    end
+    local tmp=d
+    d=c
+    c=b
+    b=add32(b, rol(add32(a,f,K[i+1],M[g+1]), S[i+1]))
+    a=tmp
+  end
+  self.a=add32(self.a,a); self.b=add32(self.b,b)
+  self.c=add32(self.c,c); self.d=add32(self.d,d)
+end
+
+function StreamMD5:update(data)
+  assert(not self.done, "StreamMD5 context already finalized")
+  assert(type(data)=="string", "StreamMD5:update expects a string")
+  self.bytes = self.bytes + #data
+  local s = self.buffer .. data
+  local full = #s - (#s % 64)
+  for i=1,full,64 do self:_block(s:sub(i,i+63)) end
+  self.buffer = s:sub(full+1)
+  return self
+end
+
+function StreamMD5:final()
+  assert(not self.done, "StreamMD5 context already finalized")
+  local originalBytes = self.bytes
+  local padLen = (56 - ((originalBytes + 1) % 64)) % 64
+  local bits = originalBytes * 8
+  local lo = bits % 4294967296
+  local hi = math.floor(bits / 4294967296) % 4294967296
+  self:update("\128" .. string.rep("\0", padLen) .. le32_bytes(lo) .. le32_bytes(hi))
+  assert(#self.buffer == 0, "MD5 finalization left a partial block")
+  self.done=true
+  local raw = le32_bytes(self.a)..le32_bytes(self.b)..le32_bytes(self.c)..le32_bytes(self.d)
+  return (raw:gsub(".", function(ch) return string.format("%02x", ch:byte()) end))
+end
+
+return StreamMD5
diff --git a/tests/engine/battle_charge_required.lua b/tests/engine/battle_charge_required.lua
new file mode 100644
index 00000000..c046639a
--- /dev/null
+++ b/tests/engine/battle_charge_required.lua
@@ -0,0 +1,345 @@
+-- Public, shared battle.charge_required hook.
+--
+-- A mod that adds weather to Gen 1 needs to let SolarBeam resolve on the
+-- turn it is selected without replacing the move, mutating private battle
+-- state, or reimplementing the damage pipeline.  This case loads a real
+-- sandboxed mod through the public SDK and drives the real Gen 1 and Gold
+-- battle engines.  It also pins each generation's empty-chain decision.
+
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+local BattleState = require("src.battle.BattleState")
+local Font = require("src.render.Font")
+local Gen2Battle = require("src.battle.gen2.Battle")
+local Gen2Mon = require("src.battle.gen2.Mon")
+local Pokemon = require("src.pokemon.Pokemon")
+local Runtime = require("src.mods.Runtime")
+local SaveData = require("src.core.SaveData")
+local TypeChart = require("src.battle.TypeChart")
+
+local function lowRoll(a)
+  return a or 0
+end
+
+local function queueHasText(battle, fragment)
+  for _, row in ipairs(battle.queue or {}) do
+    if row.text and row.text:find(fragment, 1, true) then return true end
+  end
+  return false
+end
+
+local function eventHasText(battle, fragment)
+  for _, row in ipairs(battle.events or {}) do
+    if row.kind == "message" and row.text
+        and row.text:find(fragment, 1, true) then return true end
+  end
+  return false
+end
+
+local function gen1Data()
+  local data = T.fixtures.fresh()
+  data.moves.SOLARBEAM = {
+    id = "SOLARBEAM", index = 80, name = "SOLARBEAM", type = "GRASS",
+    power = 120, accuracy = 100, pp = 10, effect = "CHARGE_EFFECT",
+  }
+  data.moves.FLY = {
+    id = "FLY", index = 81, name = "FLY", type = "FLYING",
+    power = 70, accuracy = 95, pp = 15, effect = "FLY_EFFECT",
+  }
+  data.moves.DIG = {
+    id = "DIG", index = 82, name = "DIG", type = "GROUND",
+    power = 100, accuracy = 100, pp = 10, effect = "FLY_EFFECT",
+  }
+  Font.load(data)
+  TypeChart.load(data)
+  return data
+end
+
+local function gen1Battle(data, moveId)
+  local save = SaveData.newGame()
+  save.party = { Pokemon.new(data, "FIXMON_A", 30) }
+  local move = { id = moveId, pp = 10, maxPp = 10 }
+  save.party[1].moves = { move }
+  local stack = { states = {} }
+  function stack:push(state) self.states[#self.states + 1] = state end
+  function stack:pop() return table.remove(self.states) end
+  function stack:top() return self.states[#self.states] end
+  local game = { data = data, save = save, stack = stack,
+    input = { wasPressed = function() return false end,
+              isDown = function() return false end } }
+  local battle = BattleState.newWild(game, "FIXMON_B", 20)
+  battle.rng = lowRoll
+  return battle, battle.player, battle.enemy, move
+end
+
+local G2_TYPES = {
+  NORMAL = { id = "NORMAL", index = 0, category = "physical" },
+  GRASS = { id = "GRASS", index = 22, category = "special" },
+  FLYING = { id = "FLYING", index = 2, category = "physical" },
+  GROUND = { id = "GROUND", index = 4, category = "physical" },
+}
+
+local G2_MOVES = {
+  TACKLE = { id = "TACKLE", name = "TACKLE", power = 35,
+    type = "NORMAL", accuracy = 100, pp = 35,
+    effect = "EFFECT_NORMAL_HIT" },
+  SOLARBEAM = { id = "SOLARBEAM", name = "SOLARBEAM", power = 120,
+    type = "GRASS", accuracy = 100, pp = 10,
+    effect = "EFFECT_SOLARBEAM" },
+  FLY = { id = "FLY", name = "FLY", power = 70, type = "FLYING",
+    accuracy = 95, pp = 15, effect = "EFFECT_FLY" },
+  DIG = { id = "DIG", name = "DIG", power = 60, type = "GROUND",
+    accuracy = 100, pp = 10, effect = "EFFECT_FLY" },
+}
+
+local G2_DATA = {
+  pokemon = {
+    growthRates = {
+      GROWTH_MEDIUM_FAST = { numerator = 1, denominator = 1, squared = 0,
+        linear = 0, constant = 0 },
+    },
+    MACHOP = {
+      id = "MACHOP", index = 66, name = "MACHOP",
+      baseStats = { hp = 70, attack = 80, defense = 50, speed = 35,
+        specialAttack = 35, specialDefense = 35 },
+      types = { "NORMAL", "NORMAL" }, catchRate = 180, baseExp = 75,
+      growthRate = "GROWTH_MEDIUM_FAST", genderRatio = 63,
+      levelMoves = {}, evolutions = {},
+    },
+  },
+  moves = G2_MOVES,
+  type_chart = { types = G2_TYPES, matchups = {} },
+  items = {},
+}
+
+local G2_DVS = { attack = 15, defense = 15, speed = 15, special = 15 }
+G2_DVS.hp = Gen2Mon.hpDV(G2_DVS)
+
+local function gen2Battle(moveId, weather)
+  local player = Gen2Mon.new(G2_DATA, "MACHOP", 30, { dvs = G2_DVS })
+  local move = { id = moveId, pp = 10, maxPp = 10 }
+  player.moves = { move }
+  local wild = Gen2Mon.new(G2_DATA, "MACHOP", 20, { dvs = G2_DVS })
+  wild.moves = { { id = "TACKLE", pp = 35, maxPp = 35 } }
+  local battle = Gen2Battle.new({ data = G2_DATA, party = { player },
+    wild = wild, random = function(n) return math.max(0, (n or 1) - 1) end })
+  battle.weather = weather
+  return battle, player, wild, move
+end
+
+-- No-mod parity: Red always charges a charge-capable move on initial use,
+-- spends PP only on that initial use, and resolves on the continuation.
+do
+  local run = T.sdk.loadNone()
+  local battle, player, enemy, move = gen1Battle(gen1Data(), "SOLARBEAM")
+  local hp = enemy.mon.hp
+  battle:performMove(player, enemy, move)
+  T.eq(enemy.mon.hp, hp, "Gen 1 no-mod initial SolarBeam only charges")
+  T.eq(player.charging, move, "Gen 1 no-mod stores the selected move")
+  T.eq(move.pp, 9, "Gen 1 no-mod charge spends one PP")
+  T.check(queueHasText(battle, "took in sunlight"),
+    "Gen 1 no-mod keeps the charge text")
+  battle:performMove(player, enemy, move)
+  T.check(enemy.mon.hp < hp, "Gen 1 no-mod continuation resolves damage")
+  T.eq(move.pp, 9, "Gen 1 no-mod continuation spends no second PP")
+  run.release()
+end
+
+-- No-mod parity: Gold's native answer remains weather-sensitive.  Solarbeam
+-- charges without sun and skips charge under sun.
+do
+  local run = T.sdk.loadNone({ generation = 2 })
+  local battle, player, wild, move = gen2Battle("SOLARBEAM")
+  local hp = wild.hp
+  battle:useMove(player, wild, "SOLARBEAM")
+  T.eq(wild.hp, hp, "Gold no-mod initial Solarbeam charges without sun")
+  T.eq(player.volatile.chargeMove, "SOLARBEAM",
+    "Gold no-mod stores Solarbeam without sun")
+  T.eq(move.pp, 9, "Gold no-mod charge spends one PP")
+  battle:useMove(player, wild, "SOLARBEAM")
+  T.check(wild.hp < hp, "Gold no-mod continuation resolves damage")
+  T.eq(player.volatile.chargeMove, nil,
+    "Gold no-mod continuation clears stored charge state")
+  T.eq(move.pp, 9, "Gold no-mod continuation spends no second PP")
+
+  battle, player, wild, move = gen2Battle("SOLARBEAM", "sun")
+  hp = wild.hp
+  battle:useMove(player, wild, "SOLARBEAM")
+  T.check(wild.hp < hp, "Gold no-mod sun skips Solarbeam charge")
+  T.eq(player.volatile.chargeMove, nil,
+    "Gold no-mod sun stores no charge continuation")
+  T.eq(move.pp, 9, "Gold no-mod sun still spends exactly one PP")
+  run.release()
+end
+
+local MOD = {
+  ["mods/charge_probe/manifest.json"] = [[{
+    "id": "charge_probe",
+    "name": "Charge Required Probe",
+    "version": "1.0.0",
+    "entry": "main.lua",
+    "api": 2,
+    "games": ["all"]
+  }]],
+  ["mods/charge_probe/main.lua"] = [[
+    local mod = ...
+    mod.hooks:wrap("battle.charge_required", function(nextFn, ctx)
+      mod.exports.calls = (mod.exports.calls or 0) + 1
+      mod.exports.last = {
+        battle = ctx.battle ~= nil,
+        user = ctx.user ~= nil,
+        target = ctx.target ~= nil,
+        move = ctx.move and ctx.move.id,
+        charge = ctx.charge,
+        isCalled = ctx.isCalled,
+      }
+      if ctx.move.id == "SOLARBEAM" then return false end
+      return nextFn(ctx)
+    end)
+  ]],
+}
+
+-- Public mod API, Gen 1: one conditional false resolves through the ordinary
+-- damage pipeline on the first turn.  Fly and Dig keep their vanilla charge
+-- state, invulnerability, PP, and text; the release does not call the hook.
+do
+  local run = T.sdk.loadMods({ "mods/charge_probe" }, {
+    fs = T.sdk.memfs(MOD),
+  })
+  T.eq(#run.errors, 0,
+    "the public charge hook mod loads clean (" .. tostring(run.errors[1]) .. ")")
+  local data = gen1Data()
+  local battle, player, enemy, move = gen1Battle(data, "SOLARBEAM")
+  local hp = enemy.mon.hp
+  battle:performMove(player, enemy, move)
+  T.check(enemy.mon.hp < hp,
+    "a public Gen 1 hook can resolve SolarBeam on its initial use")
+  T.eq(move.pp, 9, "the one-turn Gen 1 resolution spends one PP")
+  T.eq(player.charging, nil, "the bypass creates no Gen 1 continuation")
+  T.check(not queueHasText(battle, "took in sunlight"),
+    "the bypass emits no Gen 1 charge text")
+
+  local out = run.loader.exports.charge_probe or {}
+  T.eq(out.calls, 1, "the public Gen 1 hook fires once on initial use")
+  T.same(out.last, {
+    battle = true, user = true, target = true, move = "SOLARBEAM",
+    charge = true, isCalled = false,
+  }, "the public Gen 1 hook receives the generation-neutral context")
+
+  for _, id in ipairs({ "FLY", "DIG" }) do
+    battle, player, enemy, move = gen1Battle(data, id)
+    local beforeCalls = out.calls or 0
+    battle:performMove(player, enemy, move)
+    T.eq(player.charging, move, id .. " still charges through next(ctx)")
+    T.eq(player.invulnerable, true, id .. " still becomes invulnerable")
+    T.eq(move.pp, 9, id .. " still spends one PP on its charge turn")
+    T.check(queueHasText(battle, id == "FLY" and "flew up" or "dug a hole"),
+      id .. " still emits its charge text")
+    T.eq(out.calls, beforeCalls + 1, id .. " calls the hook on initial use")
+    battle:performMove(player, enemy, move)
+    T.eq(out.calls, beforeCalls + 1,
+      id .. " release does not call the initial-use hook again")
+    T.eq(move.pp, 9, id .. " release spends no second PP")
+  end
+
+  -- Called charge-capable moves get the same initial-use seam and say so.
+  battle, player, enemy, move = gen1Battle(data, "FLY")
+  battle:performMove(player, enemy, move, true)
+  out = run.loader.exports.charge_probe or {}
+  T.eq(out.last and out.last.isCalled, true,
+    "the Gen 1 context marks a called charge move")
+  T.eq(move.pp, 10, "a called Gen 1 charge move keeps called-move PP semantics")
+  run.release()
+end
+
+-- Public mod API, Gold: the same wrapper bypasses the ordinary no-sun charge
+-- branch, preserves one PP spend, and emits no charge text.
+do
+  local run = T.sdk.loadMods({ "mods/charge_probe" }, {
+    fs = T.sdk.memfs(MOD), generation = 2,
+  })
+  T.eq(#run.errors, 0,
+    "the shared charge hook mod loads clean on Gold")
+  local battle, player, wild, move = gen2Battle("SOLARBEAM")
+  local hp = wild.hp
+  battle:useMove(player, wild, "SOLARBEAM")
+  T.check(wild.hp < hp,
+    "the public Gold hook resolves Solarbeam on its initial use")
+  T.eq(move.pp, 9, "the one-turn Gold resolution spends one PP")
+  T.eq(player.volatile.chargeMove, nil,
+    "the bypass creates no Gold charge continuation")
+  T.check(not eventHasText(battle, "took in sunlight"),
+    "the bypass emits no Gold charge text")
+  local out = run.loader.exports.charge_probe or {}
+  T.same(out.last, {
+    battle = true, user = true, target = true, move = "SOLARBEAM",
+    charge = true, isCalled = false,
+  }, "Gold receives the same generation-neutral hook context")
+
+  local calls = out.calls
+  battle, player, wild, move = gen2Battle("DIG")
+  hp = wild.hp
+  battle:useMove(player, wild, "DIG")
+  T.eq(wild.hp, hp, "Gold next(ctx) keeps the initial charge turn")
+  T.eq(player.volatile.chargeMove, "DIG",
+    "Gold next(ctx) stores the selected charge move")
+  T.eq(player.volatile.vanished, true,
+    "Gold next(ctx) preserves semi-invulnerability")
+  T.eq(move.pp, 9, "Gold next(ctx) spends one PP on the charge turn")
+  T.eq(out.calls, calls + 1,
+    "Gold next(ctx) invokes the hook once on initial use")
+  battle:useMove(player, wild, "DIG")
+  T.check(wild.hp < hp, "Gold next(ctx) release resolves damage")
+  T.eq(out.calls, calls + 1,
+    "Gold release does not invoke the charge hook again")
+  T.eq(move.pp, 9, "Gold release spends no second PP")
+
+  calls = out.calls
+  battle, player, wild, move = gen2Battle("TACKLE")
+  battle.copyDepth = 1
+  battle:useMove(player, wild, "FLY")
+  T.eq(out.calls, calls + 1, "a called Gold charge move invokes the hook")
+  T.eq(out.last and out.last.isCalled, true,
+    "the Gold context marks a called charge move")
+  T.eq(move.pp, 10, "a called Gold move spends no known-move PP")
+  T.eq(player.volatile.chargeMove, "FLY",
+    "a called Gold charge move can keep its charge through next(ctx)")
+
+  calls = out.calls
+  battle, player, wild, move = gen2Battle("SOLARBEAM", "sun")
+  hp = wild.hp
+  battle:useMove(player, wild, "SOLARBEAM")
+  T.check(wild.hp < hp,
+    "Gold native sun still resolves before the public charge decision")
+  T.eq(out.calls, calls,
+    "the hook does not run when the active rules already skip charge")
+  run.release()
+end
+
+-- Guard parity: with no subscriber, neither generation reaches Runtime.call;
+-- both take their vanilla decision without constructing/dispatching a ctx.
+do
+  local battle, player, enemy, move = gen1Battle(gen1Data(), "SOLARBEAM")
+  local battle2, player2, enemy2 = gen2Battle("SOLARBEAM")
+  local oldWants, oldCall = Runtime.wantsHook, Runtime.call
+  Runtime.wantsHook = function(name)
+    T.eq(name, "battle.charge_required", "the Gen 1 guard checks the hook name")
+    return false
+  end
+  Runtime.call = function()
+    error("unsubscribed charge hot path dispatched", 0)
+  end
+  local ok, err = pcall(battle.performMove, battle, player, enemy, move)
+  T.check(ok, "the guarded Gen 1 hot path does not dispatch: " .. tostring(err))
+
+  Runtime.wantsHook = function(name)
+    T.eq(name, "battle.charge_required", "the Gold guard checks the hook name")
+    return false
+  end
+  ok, err = pcall(battle2.useMove, battle2, player2, enemy2, "SOLARBEAM")
+  T.check(ok, "the guarded Gold hot path does not dispatch: " .. tostring(err))
+  Runtime.wantsHook, Runtime.call = oldWants, oldCall
+end
+
+T.finish("battle charge required")
diff --git a/tests/engine/gate_gen2_mod_api.lua b/tests/engine/gate_gen2_mod_api.lua
index beabb51c..01558e97 100644
--- a/tests/engine/gate_gen2_mod_api.lua
+++ b/tests/engine/gate_gen2_mod_api.lua
@@ -402,7 +402,8 @@ local GEN2_HOOKS = {
   "ui.pc.items", "ui.list_menu",
   "transition.style",
   -- battle
-  "battle.damage", "battle.crit", "battle.accuracy", "battle.turn_order",
+  "battle.damage", "battle.crit", "battle.accuracy",
+  "battle.charge_required", "battle.turn_order",
   "battle.enemy_action", "battle.run", "battle.exp_award", "exp.gain",
   "catch.rate", "trainer.party",
   -- one wrap cancels or forces an evolution in either game: Gold passes `data`
diff --git a/tests/engine/mod_import_access_parity_test.lua b/tests/engine/mod_import_access_parity_test.lua
new file mode 100644
index 00000000..fc2f7c73
--- /dev/null
+++ b/tests/engine/mod_import_access_parity_test.lua
@@ -0,0 +1,42 @@
+-- No-mod and API-v1 parity coverage for additive mod.imports/mod.cache.
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+
+-- No mod installed: no generated cache namespace is touched.
+local emptyFiles = {}
+local none = T.sdk.loadNone({ fs = T.sdk.memfs(emptyFiles) })
+T.eq(#none.errors, 0, "zero-mod load remains clean")
+for path in pairs(emptyFiles) do
+  T.check(path:sub(1, 10) ~= "mod_cache/",
+    "zero-mod load creates no installation cache data")
+end
+none.release()
+
+-- Existing API-v1 style file access still behaves exactly as before. The new
+-- facades are additive members; mod:read remains the same scoped read path.
+local files = {
+  ["mods/v1_read_probe/manifest.json"] = [[{
+    "id": "v1_read_probe",
+    "name": "V1 Read Probe",
+    "version": "1.0.0",
+    "entry": "main.lua",
+    "api": 1
+  }]],
+  ["mods/v1_read_probe/main.lua"] = [[
+    local mod = ...
+    mod.exports.payload = mod:read("payload.txt")
+    mod.exports.hasImports = type(mod.imports) == "table"
+    mod.exports.hasCache = type(mod.cache) == "table"
+  ]],
+  ["mods/v1_read_probe/payload.txt"] = "unchanged-v1-read",
+}
+local run = T.sdk.loadMods({ "mods/v1_read_probe" }, { fs = T.sdk.memfs(files) })
+T.eq(#run.errors, 0, "API-v1 probe still loads")
+local out = run.loader.exports.v1_read_probe
+T.eq(out.payload, "unchanged-v1-read", "mod:read keeps its v1 behavior")
+T.eq(out.hasImports, true, "new import facade is additive")
+T.eq(out.hasCache, true, "new cache facade is additive")
+run.release()
+
+T.finish("mod_import_access_parity")
diff --git a/tests/engine/mod_import_access_test.lua b/tests/engine/mod_import_access_test.lua
new file mode 100644
index 00000000..f861e73f
--- /dev/null
+++ b/tests/engine/mod_import_access_test.lua
@@ -0,0 +1,105 @@
+-- Public mod-API coverage for bounded validated imports + installation cache.
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+
+local digest = "00000000000000000000000000000000"
+local files = {
+  ["mods/import_api_probe/manifest.json"] = [[{
+    "id": "import_api_probe",
+    "name": "Import API Probe",
+    "version": "1.0.0",
+    "entry": "main.lua",
+    "api": 2,
+    "required_imports": [{
+      "id": "disc",
+      "name": "Disc",
+      "file": "source.iso",
+      "md5": ["00000000000000000000000000000000"],
+      "size": 16
+    }],
+    "optional_imports": [{
+      "id": "optional",
+      "name": "Optional",
+      "file": "optional.bin",
+      "md5": ["11111111111111111111111111111111"],
+      "size": 4,
+      "required": false
+    }]
+  }]],
+  ["mods/import_api_probe/main.lua"] = [[
+    local mod = ...
+    local info, infoErr = mod.imports:info("disc")
+    local slice, sliceErr = mod.imports:read("disc", 4, 6)
+    local oob, oobErr = mod.imports:read("disc", 15, 2)
+    local missing, missingErr = mod.imports:info("optional")
+    local undeclared, undeclaredErr = mod.imports:read("not_declared", 0, 1)
+
+    local wrote, writeErr = mod.cache:write("extract/v1/probe.bin", "abc")
+    local cached, readErr = mod.cache:read("extract/v1/probe.bin")
+    local cacheInfo = mod.cache:info("extract/v1/probe.bin")
+    local escaped = pcall(function() mod.cache:write("../escape.bin", "x") end)
+
+    mod.exports.result = {
+      info = info, infoErr = infoErr,
+      slice = slice, sliceErr = sliceErr,
+      oob = oob, oobErr = oobErr,
+      missing = missing, missingErr = missingErr,
+      undeclared = undeclared, undeclaredErr = undeclaredErr,
+      wrote = wrote, writeErr = writeErr,
+      cached = cached, readErr = readErr,
+      cacheInfo = cacheInfo,
+      escaped = escaped,
+    }
+  ]],
+  ["mods/import_api_probe/baseroms/source.iso"] = "0123456789abcdef",
+  ["mods/import_api_probe/baseroms/.required-import-disc.validated"] =
+    "v1\n" .. digest .. "\n16\n1\n",
+}
+
+local baseFs = T.sdk.memfs(files)
+local oldInfo = baseFs.getInfo
+function baseFs.getInfo(path)
+  local info = oldInfo(path)
+  if info and info.type == "file" then
+    return { type = "file", size = #(files[path] or ""), modtime = 1 }
+  end
+  return info
+end
+function baseFs.readRange(path, offset, length)
+  local body = files[path]
+  if not body then return nil end
+  return body:sub(offset + 1, offset + length)
+end
+function baseFs.createDirectory() return true end
+function baseFs.remove(path) files[path] = nil return true end
+
+local run = T.sdk.loadMods({ "mods/import_api_probe" }, { fs = baseFs })
+T.eq(#run.errors, 0,
+  "the import/cache probe loads through the production Loader")
+
+local out = run.loader.exports.import_api_probe.result
+T.check(type(out.info) == "table", "declared validated import has info")
+T.eq(out.info.size, 16, "import info reports stored size")
+T.eq(out.slice, "456789", "bounded read seeks into the validated import")
+T.eq(out.sliceErr, nil, "bounded read has no error")
+T.eq(out.oob, nil, "out-of-bounds read is refused")
+T.check(type(out.oobErr) == "string" and out.oobErr:find("out of bounds", 1, true),
+  "out-of-bounds read explains the refusal")
+T.eq(out.missing, nil, "missing optional import is not exposed")
+T.check(type(out.missingErr) == "string", "missing optional import returns an error")
+T.eq(out.undeclared, nil, "undeclared import id is refused")
+T.check(type(out.undeclaredErr) == "string"
+    and out.undeclaredErr:find("undeclared", 1, true),
+  "undeclared import refusal is explicit")
+
+T.check(out.wrote == true, "installation cache write succeeds")
+T.eq(out.cached, "abc", "installation cache read returns exact bytes")
+T.eq(out.cacheInfo and out.cacheInfo.size, 3, "installation cache info is scoped")
+T.eq(out.escaped, false, "cache traversal is rejected by the public facade")
+T.eq(files["mod_cache/import_api_probe/extract/v1/probe.bin"], "abc",
+  "cache bytes live under the calling mod id")
+T.eq(files["escape.bin"], nil, "cache traversal created nothing outside its root")
+
+run.release()
+T.finish("mod_import_access")
diff --git a/tests/engine/required_import_streaming_test.lua b/tests/engine/required_import_streaming_test.lua
new file mode 100644
index 00000000..1de44ddf
--- /dev/null
+++ b/tests/engine/required_import_streaming_test.lua
@@ -0,0 +1,183 @@
+-- Regression for large raw required imports: direct source -> engine-owned
+-- baseroms destination, incremental MD5, no whole-file staging requirement.
+package.path = "./?.lua;./?/init.lua;" .. package.path
+if not _G.love then _G.love = require("tests.love_stub") end
+
+local T = require("tests.modkit")
+local RomImporter = require("src.import.RomImporter")
+local RequiredImports = require("src.mods.RequiredImports")
+
+-- The stock headless filesystem intentionally omits love.filesystem.newFile.
+-- Add the smallest streaming-file facade this transport path needs so the
+-- regression drives the same seek/read/write API production LÖVE provides.
+local oldNewFile = love.filesystem.newFile
+local oldGetInfo = love.filesystem.getInfo
+love.filesystem.newFile = function(path)
+  local body, pos, mode = love.filesystem.read(path) or "", 1, nil
+  local file = {}
+  function file:open(m)
+    mode = m
+    if m == "w" then body, pos = "", 1 else pos = 1 end
+    return true
+  end
+  function file:read(n)
+    local out = body:sub(pos, pos + n - 1)
+    pos = pos + #out
+    if out == "" then return nil end
+    return out
+  end
+  function file:write(bytes)
+    if mode ~= "w" then return nil, "not open for write" end
+    body = body:sub(1, pos - 1) .. bytes .. body:sub(pos + #bytes)
+    pos = pos + #bytes
+    love.filesystem.write(path, body)
+    return true
+  end
+  function file:seek(offset) pos = offset + 1 return offset end
+  function file:getSize() return #body end
+  function file:close()
+    if mode == "w" then love.filesystem.write(path, body) end
+    mode = nil
+    return true
+  end
+  return file
+end
+love.filesystem.getInfo = function(path, filter)
+  local info = oldGetInfo(path, filter)
+  if info and info.type == "file" then
+    local bytes = love.filesystem.read(path) or ""
+    return { type = "file", size = #bytes, modtime = 1 }
+  end
+  return info
+end
+
+local source = "required_import_streaming_source.tmp"
+local f = assert(io.open(source, "wb"))
+f:write("abc")
+f:close()
+
+local manifest = {
+  id = "stream_probe",
+  name = "Stream Probe",
+  path = "mods/stream_probe",
+  required_imports = {
+    { id = "source", name = "Source", file = "source.bin", format = "raw",
+      size = 3, md5 = { "900150983cd24fb0d6963f7d28e17f72" } },
+  },
+  optional_imports = {},
+}
+
+local importer = setmetatable({
+  mods = { { id = "stream_probe", manifest = manifest } },
+  requiredImportNotice = nil,
+  modNotice = nil,
+  _refreshMods = function(self) self._refreshed = true end,
+}, RomImporter)
+
+-- Reproduce the Windows failure seen with a 1.46 GiB optical-disc image:
+-- after the user accepts the "Large import" confirmation, the old path calls
+-- love.filesystem.read(source) and attempts to materialize the entire source as
+-- one Lua string. A large raw source must go straight to the streaming branch.
+local ordinaryLoveRead = love.filesystem.read
+local forbiddenWholeSourceReads = 0
+love.filesystem.read = function(path, ...)
+  if path == source then
+    forbiddenWholeSourceReads = forbiddenWholeSourceReads + 1
+    error("large external required import used whole-file love.filesystem.read")
+  end
+  return ordinaryLoveRead(path, ...)
+end
+
+-- Exercise the exact large-file branch with tiny fixture bytes by lowering the
+-- threshold for this test. Production keeps the 128 MiB confirmation/streaming
+-- threshold; the copy/hash algorithm is identical.
+local oldWarn = RequiredImports.LARGE_WARN_BYTES
+RequiredImports.LARGE_WARN_BYTES = 2
+local ok = importer:_importRequiredSource("stream_probe", "source", source, true)
+RequiredImports.LARGE_WARN_BYTES = oldWarn
+love.filesystem.read = ordinaryLoveRead
+
+T.eq(ok, true, "large raw required import streams successfully")
+T.eq(forbiddenWholeSourceReads, 0,
+  "post-confirm large import never materializes the external source as one Lua string")
+T.eq(love.filesystem.read("mods/stream_probe/baseroms/source.bin"), "abc",
+  "streamed destination preserves exact source bytes")
+T.eq(importer.requiredImportNotice, nil, "successful stream leaves no import error")
+T.eq(importer._refreshed, true, "successful stream refreshes the mod list")
+
+local CacheFs = require("src.import.CacheFs")
+
+-- A thrown writer error must not leak the temporary empty CacheFs prefix.
+local workingNewFile = love.filesystem.newFile
+local workingPrefix = CacheFs.prefix
+CacheFs.prefix = "sentinel/"
+love.filesystem.newFile = function(path)
+  local file = workingNewFile(path)
+  if path == "mods/stream_probe/baseroms/source.bin" then
+    function file:write()
+      error("forced writer failure")
+    end
+  end
+  return file
+end
+importer.requiredImportNotice = nil
+RequiredImports.LARGE_WARN_BYTES = 2
+local failedWrite = importer:_importRequiredSource(
+  "stream_probe", "source", source, true)
+RequiredImports.LARGE_WARN_BYTES = oldWarn
+T.eq(failedWrite, nil, "thrown streaming writer error is contained")
+T.eq(CacheFs.prefix, "sentinel/",
+  "streaming writer error restores CacheFs.prefix")
+love.filesystem.newFile = workingNewFile
+CacheFs.prefix = workingPrefix
+
+-- acceptStoredDigest has its own prefix switch for marker/receipt I/O.
+-- Even an unexpected CacheFs failure must restore the caller's prefix.
+love.filesystem.write("mods/stream_probe/baseroms/source.bin", "abc")
+local workingRemove = CacheFs.remove
+CacheFs.prefix = "sentinel/"
+CacheFs.remove = function()
+  error("forced marker removal failure")
+end
+local accepted = RequiredImports.acceptStoredDigest(
+  manifest, "source", "900150983cd24fb0d6963f7d28e17f72", love.filesystem)
+T.eq(accepted, nil, "acceptStoredDigest contains CacheFs failure")
+T.eq(CacheFs.prefix, "sentinel/",
+  "acceptStoredDigest failure restores CacheFs.prefix")
+CacheFs.remove = workingRemove
+CacheFs.prefix = workingPrefix
+
+-- Native sources are rejected cleanly if seek-to-start fails after the
+-- size probe; never return a handle left sitting at EOF.
+local realIoOpen = io.open
+local fakeCloses = 0
+io.open = function(path, mode)
+  if path ~= source then return realIoOpen(path, mode) end
+  local calls = 0
+  return {
+    seek = function(_, whence)
+      calls = calls + 1
+      if whence == "end" then return 3 end
+      if whence == "set" then return nil, "forced rewind failure" end
+      return nil, "unexpected seek"
+    end,
+    close = function() fakeCloses = fakeCloses + 1 end,
+  }
+end
+importer.requiredImportNotice = nil
+RequiredImports.LARGE_WARN_BYTES = 2
+local failedSeek = importer:_importRequiredSource(
+  "stream_probe", "source", source, true)
+RequiredImports.LARGE_WARN_BYTES = oldWarn
+io.open = realIoOpen
+T.eq(failedSeek, nil, "failed native rewind rejects import source")
+T.eq(fakeCloses >= 2, true,
+  "failed native rewind closes probed source handles")
+
+love.filesystem.remove("mods/stream_probe/baseroms/source.bin")
+love.filesystem.remove("mods/stream_probe/baseroms/source.iso")
+os.remove(source)
+love.filesystem.newFile = oldNewFile
+love.filesystem.getInfo = oldGetInfo
+
+T.finish("required_import_streaming")
diff --git a/tests/engine/stream_md5_test.lua b/tests/engine/stream_md5_test.lua
new file mode 100644
index 00000000..c75879b3
--- /dev/null
+++ b/tests/engine/stream_md5_test.lua
@@ -0,0 +1,33 @@
+-- Incremental MD5 vectors used by large required-import streaming.
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+-- Plain Lua runners may expose bit32 while production LuaJIT exposes bit.
+if not rawget(_G, "bit") and not rawget(_G, "bit32") then
+  local ok, bit32 = pcall(require, "bit32")
+  if ok then _G.bit32 = bit32 end
+end
+
+local T = require("tests.modkit")
+local MD5 = require("src.mods.StreamMD5")
+
+local vectors = {
+  { "", "d41d8cd98f00b204e9800998ecf8427e" },
+  { "a", "0cc175b9c0f1b6a831c399e269772661" },
+  { "abc", "900150983cd24fb0d6963f7d28e17f72" },
+  { "message digest", "f96b697d7cb7938d525a2f31aaf161d0" },
+  { "abcdefghijklmnopqrstuvwxyz", "c3fcd3d76192e4007dfb496cca67e13b" },
+}
+
+for _, row in ipairs(vectors) do
+  local ctx = MD5.new()
+  for i = 1, #row[1], 3 do ctx:update(row[1]:sub(i, i + 2)) end
+  T.eq(ctx:final(), row[2], "incremental MD5 vector: " .. row[1])
+end
+
+-- Cross a large number of block boundaries without building one giant string.
+local million = MD5.new()
+for _ = 1, 1000 do million:update(string.rep("a", 1000)) end
+T.eq(million:final(), "7707d6ae4e027c70eea2a935c2296f21",
+  "RFC 1321 million-a vector")
+
+T.finish("stream_md5")