fix(preview): refuse ~/ in a Docker case; document the folder-route gate

A Docker case is a local session for the file routes, but `~` inside the
container is the container's own seeded home. Expanding `~/x.png` on the host
opened a different file than the one the agent printed. The attachment POST
and POST …/folders now answer 400 for `~/` when the session has `docker` set
(absolute paths are unaffected: the workspace is a bind mount).

Docs: the resolved-target gate, the route-parameter limit, the listing join
rule and the Docker `~/` refusal in architecture-invariants.md,
security-architecture.md and CLAUDE.md.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -299,7 +299,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 
 **Prompt uploads** (`POST /api/sessions/:id/paste-image`; client wiring in `image-input.js` and `keyboard-accessory.js`): a pasted file is written to `<workspace>/.codeman-uploads/` and its path lands on the prompt as unsent text. The folder is IN the workspace because that is the only path identical for a local and a container agent, FLAT because `<workspace>/.codeman/` would BE the data dir when the workspace is the home directory, and self-ignoring through a `.gitignore` of `*` written ONCE with `wx` (a file already there is the user's and is never overwritten; the user's own ignore file is never touched). ⚠️ The directory names live ONLY in `paste-image-gc.ts` (`UPLOAD_DIR_NAMES`): the pre-move `.claude-images/` receives nothing but stays readable for one release, so the GC sweep and the delete cleanup (through `uploadDirs()`) and the image watcher's ignore filter (reading the names) cover BOTH; retire the legacy entry there, never by hand elsewhere. ⚠️ `uploadDirs()` is async and probes the workspace BOUNDED first (`probePathKind()`, the #516 rule: an `unknown` path is skipped, never touched; the sweep keeps the stall cap and the delete passes `pastCap`), then returns only REAL directories (lstat, so a planted symlink is never one), none that is or contains `getDataDir()` (one strictly inside it only holds uploads and is listed), and none for a remote session, since both consumers delete; the check is made at list time, and the same-user race after it is accepted. A remote (SSH) session is refused (400) before any disk touch: its `workingDir` is the remote path, so the file would land on THIS host where the agent cannot read it. → [architecture-invariants#buffers-uploads-and-terminal-history](docs/architecture-invariants.md#buffers-uploads-and-terminal-history)
 
-**File-path links (terminal + chat)**: a path an agent prints is clickable on BOTH surfaces and opens the file-preview overlay. ⚠️ ONE pattern (`FILE_PATH_LINK_PATTERN` / `absoluteFilePathPattern()` in constants.js) feeds the xterm link provider AND `_linkifyFilePaths()`, a fresh instance per call (`lastIndex`). Both call `findFilePathLinks()`, which adds `~/`, relative and folder paths without overlapping a rooted match or a URL; a relative path resolves against `workingDir` (`resolveLinkedFilePath`), `~/` only server-side on the session's host (attachment route), and `terminalPathLine()` joins a path a program hard-wrapped short of the edge. ⚠️ A folder link opens the **folder grid**: `POST /api/sessions/:id/folders` guards + GRANTS the folder (`folder-listing.ts`, own registry, never the 200-capped attachment registry), files come by bare name via `…/folders/:folderId/files/:name/*` through `resolveServableAttachmentPath`, so no browser request carries a path. The chat linkifier walks TEXT NODES with DOM APIs, never rebuilds sanitized markup as a string. ⚠️ An out-of-workspace path goes through the ATTACHMENT routes (`POST /api/sessions/:id/attachments` with `notify: false`), never by widening `file-content`/`file-raw` or `file-stream-manager`'s `tail -f` allowlist. ⚠️ `TEXT_ATTACHMENT_EXTENSIONS` IS `EDITABLE_EXTENSIONS` (never a second list), and widening READ must never widen RUN: `html`/`htm`/`svg` stay download-only, other text is inert `text/plain`+`nosniff`. Media extensions are single-sourced in `attachment-registry.ts`. ⚠️ **XLSX previews parse in the BROWSER**, never on the server: `spreadsheet-preview.js` fetches the raw route with `?preview=true` (413 above `MAX_XLSX_BROWSER_PREVIEW_BYTES`, 10 MB) and hands the bytes to `spreadsheet-preview-worker.js`, the only place the pinned `exceljs`/`fflate` vendor bundles load (never on page load). `admitXlsx()` caps the ZIP before ExcelJS runs, counting what ExcelJS will EXPAND as well as what it reads (a merge costs its area, a `<col>` past 16384 is refused, validations are never parsed via `ignoreNodes`, and defined names are never expanded: the worker stubs `_definedNames.model`). ⚠️ The INDEX a row or sheet claims is bounded too, since ExcelJS allocates and walks up to it: a `<row r>` outside 1-1048576 and an `xl/workbook.xml` `<sheet sheetId>` above `LIMITS.maxSheetId` (65535) are refused, and `sendTile` reuses the merges read at load (`mergesById`), never `sheet.model`, which rebuilds the whole sheet. ⚠️ The COLUMN index costs the same way (a row's cells live at `_cells[col - 1]`, so one `XFD` cell makes ExcelJS's `eachRow`/`eachCell`/`hasValues` visit 16,384 slots per row): `worksheetMetadata` builds each sheet's row and cell index from the keys that exist (`Object.keys` of `_rows` and `_cells`, skipping falsy and `Null`-type cells as `eachCell({ includeEmpty: false })` does), reads row heights in that pass and merges from `sheet._merges`, and `sendTile` reads cells from that index (`populatedRowsById`); never call ExcelJS's dense `eachRow`/`eachCell` there. `parseThemePalette` returns the default palette for a theme above 64 KB (64 * 1024 characters), since its patterns are quadratic on unclosed tags. ⚠️ Merges are capped per sheet (`LIMITS.maxMergesPerSheet`, 2,000) AND workbook-wide (`LIMITS.maxMerges`, 10,000), refused as `merge-limit` before ExcelJS loads, since ExcelJS's `_mergeCellsInternal` checks each merge against every earlier one on its sheet (quadratic). Every `<numFmt>` in `xl/styles.xml` is read with `readTagAttributes()` and refused (`number-format`) when its decoded `formatCode` is over 255 characters or has a `[` after its last `]`: ExcelJS's `isDateFmt` rescans to the end of the code per unclosed `[` once per numeric cell, and the code is echoed into the notice bar. ⚠️ `formatCellValue` caps every cell's display text at `LIMITS.maxCellTextChars` (1,000, ellipsis, never splitting a surrogate pair) for every value shape (rich text, hyperlink text, formula source, errors), since structured clone copies each tile cell's whole string to the page and the load timeout no longer covers tiles. `richTextPrefix` also visits at most `maxCellTextChars + 1` runs, not only keeps that much text: an empty `<r/>` adds nothing, so a shared string of a million empty runs was walked whole per cell, per tile (56 s a tile). ⚠️ Every part ExcelJS parses (all but the pure-bytes `xl/media/<name>.<ext>`) is also charged per START TAG against `LIMITS.maxElements` (2,000,000, refused as `element-limit`): ExcelJS builds an object per element in sharedStrings, styles, comments, drawings, VML and tables too, and empty stored blocks pad a deflate stream past the ratio cap, so 8.3M empty `<r/>` runs in a 375 KB file cost 570 MB of heap. ⚠️ Admission keys every entry on the name ExcelJS will SEE (`excelJsEntryName()`: JSZip's `.`/`..`/empty-segment resolution, then one leading `/` stripped), refuses two entries thaLine truncated
+**File-path links (terminal + chat)**: a path an agent prints is clickable on BOTH surfaces and opens the file-preview overlay. ⚠️ ONE pattern (`FILE_PATH_LINK_PATTERN` / `absoluteFilePathPattern()` in constants.js) feeds the xterm link provider AND `_linkifyFilePaths()`, a fresh instance per call (`lastIndex`). Both call `findFilePathLinks()`, which adds `~/`, relative and folder paths without overlapping a rooted match or a URL; a relative path resolves against `workingDir` (`resolveLinkedFilePath`), `~/` only server-side on the session's host (attachment route), and `terminalPathLine()` joins a path a program hard-wrapped short of the edge. ⚠️ A folder link opens the **folder grid**: `POST /api/sessions/:id/folders` guards + GRANTS the folder (`folder-listing.ts`, own registry, never the 200-capped attachment registry), files come by bare name via `…/folders/:folderId/files/:name/*` through `resolveServableAttachmentPath` plus the same extension/regular-file gate on the symlink's resolved target, so no browser request carries a path; `~/` is refused in a Docker case (the container's home is not this host's). The chat linkifier walks TEXT NODES with DOM APIs, never rebuilds sanitized markup as a string. ⚠️ An out-of-workspace path goes through the ATTACHMENT routes (`POST /api/sessions/:id/attachments` with `notify: false`), never by widening `file-content`/`file-raw` or `file-stream-manager`'s `tail -f` allowlist. ⚠️ `TEXT_ATTACHMENT_EXTENSIONS` IS `EDITABLE_EXTENSIONS` (never a second list), and widening READ must never widen RUN: `html`/`htm`/`svg` stay download-only, other text is inert `text/plain`+`nosniff`. Media extensions are single-sourced in `attachment-registry.ts`. ⚠️ **XLSX previews parse in the BROWSER**, never on the server: `spreadsheet-preview.js` fetches the raw route with `?preview=true` (413 above `MAX_XLSX_BROWSER_PREVIEW_BYTES`, 10 MB) and hands the bytes to `spreadsheet-preview-worker.js`, the only place the pinned `exceljs`/`fflate` vendor bundles load (never on page load). `admitXlsx()` caps the ZIP before ExcelJS runs, counting what ExcelJS will EXPAND as well as what it reads (a merge costs its area, a `<col>` past 16384 is refused, validations are never parsed via `ignoreNodes`, and defined names are never expanded: the worker stubs `_definedNames.model`). ⚠️ The INDEX a row or sheet claims is bounded too, since ExcelJS allocates and walks up to it: a `<row r>` outside 1-1048576 and an `xl/workbook.xml` `<sheet sheetId>` above `LIMITS.maxSheetId` (65535) are refused, and `sendTile` reuses the merges read at load (`mergesById`), never `sheet.model`, which rebuilds the whole sheet. ⚠️ The COLUMN index costs the same way (a row's cells live at `_cells[col - 1]`, so one `XFD` cell makes ExcelJS's `eachRow`/`eachCell`/`hasValues` visit 16,384 slots per row): `worksheetMetadata` builds each sheet's row and cell index from the keys that exist (`Object.keys` of `_rows` and `_cells`, skipping falsy and `Null`-type cells as `eachCell({ includeEmpty: false })` does), reads row heights in that pass and merges from `sheet._merges`, and `sendTile` reads cells from that index (`populatedRowsById`); never call ExcelJS's dense `eachRow`/`eachCell` there. `parseThemePalette` returns the default palette for a theme above 64 KB (64 * 1024 characters), since its patterns are quadratic on unclosed tags. ⚠️ Merges are capped per sheet (`LIMITS.maxMergesPerSheet`, 2,000) AND workbook-wide (`LIMITS.maxMerges`, 10,000), refused as `merge-limit` before ExcelJS loads, since ExcelJS's `_mergeCellsInternal` checks each merge against every earlier one on its sheet (quadratic). Every `<numFmt>` in `xl/styles.xml` is read with `readTagAttributes()` and refused (`number-format`) when its decoded `formatCode` is over 255 characters or has a `[` after its last `]`: ExcelJS's `isDateFmt` rescans to the end of the code per unclosed `[` once per numeric cell, and the code is echoed into the notice bar. ⚠️ `formatCellValue` caps every cell's display text at `LIMITS.maxCellTextChars` (1,000, ellipsis, never splitting a surrogate pair) for every value shape (rich text, hyperlink text, formula source, errors), since structured clone copies each tile cell's whole string to the page and the load timeout no longer covers tiles. `richTextPrefix` also visits at most `maxCellTextChars + 1` runs, not only keeps that much text: an empty `<r/>` adds nothing, so a shared string of a million empty runs was walked whole per cell, per tile (56 s a tile). ⚠️ Every part ExcelJS parses (all but the pure-bytes `xl/media/<name>.<ext>`) is also charged per START TAG against `LIMITS.maxElements` (2,000,000, refused as `element-limit`): ExcelJS builds an object per element in sharedStrings, styles, comments, drawings, VML and tables too, and empty stored blocks pad a deflate stream past the ratio cap, so 8.3M empty `<r/>` runs in a 375 KB file cost 570 MB of heap. ⚠️ Admission keys every entryLine truncated
 
 **Filesystem path picker** (Link Existing "Browse" + the mobile keyboard's `📁 Path` key): lazy one-directory browsing via `GET /api/filesystem/browse`, with `GET /api/filesystem/preview` for the tapped file. Inserts the path **without** Enter, so the prompt is never submitted; the sibling `⌫ All` key clears only the unsent prompt and must never send the agent's `/clear`. ⚠️ This is a **second file-serving surface and inherits neither the attachment confinement nor its ownership scoping** — it allowlists Home, `CASES_DIR`, `/mnt/d` and `CODEMAN_FILE_PICKER_ROOTS`, blocks sensitive trees, and rejects symlink escapes **after** `realpath`. ⚠️ The optional `sessionId` is an ownership boundary that must be `canAccessOwned`-checked by hand (it does not go through `findSessionOrFail`), and in multi-user mode a non-admin gets only their own `userSpacePath` as a root: per-user spaces live INSIDE `homedir()`, so a `Home` root exposes every other user's workspace. Previews go through the same global conversion limiter, and Markdown/TXT/JSON are served as inert `text/plain`. → [architecture-invariants#filesystem-path-picker](docs/architecture-invariants.md#filesystem-path-picker)
 

docs/architecture-invariants.md

@@ -373,9 +373,9 @@ A file path an agent prints is a link on both surfaces it can appear on, and cli
 
 ⚠️ **The terminal routes an out-of-workspace path to the preview, not the log viewer.** The log viewer spawns `tail -f` and allows only the workspace, `/var/log` and `~/logs`, so an external `.log`/`.json`/code path answered `Path must be within working directory or allowed log directories` while the SAME path clicked in the response viewer previewed fine. `activate()` now checks `_isExternalPreviewPath` alongside `previewsInFileViewer`. In-workspace text keeps the tail viewer, which is the point of it (live follow); nothing widened `file-stream-manager`'s allowlist, so no `tail -f` is spawned on an arbitrary host path.
 
-**Path forms beyond the rooted one.** `findFilePathLinks(text)` (constants.js) is the single entry point both consumers call; it returns the rooted matches first, then `~/` and relative paths (`RELATIVE_FILE_PATH_LINK_PATTERN`, same extension list, pinned equal by `test/link-provider-regex.test.ts`), then folder paths, each only where it overlaps neither an earlier match nor an `http(s)` URL. A relative match must start at a boundary (line start, whitespace, quote, bracket, `=`, `,`, `>`), so it can never begin inside a word, an absolute path or a URL; brackets, `=` and `,` end it (`(shot.png)`, `OUT=shots/a.png`). `resolveLinkedFilePath()` resolves a relative path against the session's `workingDir` (`.`/`..` collapsed, so `../x.png` lands outside and routes like any external path) and passes absolute and `~/` paths through. ⚠️ `~` is the home of the SESSION'S host, which only the server knows: `~/` paths always take the attachment route, where `registerExternalAttachment` expands them (`homedir()` locally, `$HOME` inside the remote probe script), and the guard runs on the expanded, realpath-resolved path as before. ⚠️ Programs hard-wrap their own output short of the terminal edge (Claude Code breaks tool output at 59-118 columns), so xterm's `isWrapped` never fires. `terminalPathLine()` (link provider only; touch selection keeps `terminalLogicalLine`) joins the next row when the previous row ends in a path token with a `/` and no extension and the join reaches an extension; a row that starts a new rooted or `~/` path is never joined, a 3+ row chain is kept only if a later row completes the path, and the broken row must be at least as long as the continuing one (keeps `cd /mnt/foo` + a longer next line apart). Tests: `test/file-path-link-forms.test.ts`.
+**Path forms beyond the rooted one.** `findFilePathLinks(text)` (constants.js) is the single entry point both consumers call; it returns the rooted matches first, then `~/` and relative paths (`RELATIVE_FILE_PATH_LINK_PATTERN`, same extension list, pinned equal by `test/link-provider-regex.test.ts`), then folder paths, each only where it overlaps neither an earlier match nor an `http(s)` URL. A relative match must start at a boundary (line start, whitespace, quote, bracket, `=`, `,`, `>`), so it can never begin inside a word, an absolute path or a URL; brackets, `=` and `,` end it (`(shot.png)`, `OUT=shots/a.png`). `resolveLinkedFilePath()` resolves a relative path against the session's `workingDir` (`.`/`..` collapsed, so `../x.png` lands outside and routes like any external path) and passes absolute and `~/` paths through. ⚠️ `~` is the home of the SESSION'S host, which only the server knows: `~/` paths always take the attachment route, where `registerExternalAttachment` expands them (`homedir()` locally, `$HOME` inside the remote probe script), and the guard runs on the expanded, realpath-resolved path as before. ⚠️ Programs hard-wrap their own output short of the terminal edge (Claude Code breaks tool output at 59-118 columns), so xterm's `isWrapped` never fires. `terminalPathLine()` (link provider only; touch selection keeps `terminalLogicalLine`) joins the next row when the previous row ends in a path token with a `/` and no extension and the join reaches an extension; a row that starts a new path is never joined: rooted or `~/`, `./`/`../`, or a relative one that opens on the same top directory the broken token did (the next entry of `git ls-files`/`find`/`ls -R`: `src/components` + `src/index.ts` are two paths, not `src/componentssrc/index.ts`), while a wrapped path continues INSIDE a name, so `…/captures/2` + `026-10-10/…` still joins; a 3+ row chain is kept only if a later row completes the path, and the broken row must be at least as long as the continuing one (keeps `cd /mnt/foo` + a longer next line apart). Tests: `test/file-path-link-forms.test.ts`.
 
-**Folder grid: a folder is granted, then served by bare file name.** A folder path (rooted or `~/` whose last segment has no extension, relative only with a trailing `/`; `FOLDER_PATH_LINK_PATTERN` + `folderLinkPath()`) opens `openFolderGrid()` (panels-ui.js), as does the preview's "Show folder" button. `POST /api/sessions/:id/folders {path}` (`src/folder-listing.ts`) resolves the folder (locally a bounded `probePathKind(…, { pastCap: true })` first, then async `fs.realpath`; remotely one ssh round trip via `remoteListFolder`, through `runWithRemoteSshLimit`), runs the attachment guard on it (blocklist, `confineToWorkspace`, and in multi-user mode `folderAllowedForUser`: a non-admin only inside their own `userSpacePath` or the session's `workingDir`, as the filesystem path picker), locally BEFORE reading it, lists non-hidden subfolders and files of a supported attachment type (each file also blocklist-checked, newest first, capped at `MAX_FOLDER_ENTRIES`), and GRANTS it an id. Files are then fetched as `GET …/folders/:folderId/files/:name/(raw|preview|thumbnail)`: `:name` must be a bare file name of a supported type (no `/`, `\`, NUL, no leading `.`, since the listing hides those), the local file is probed bounded (`unknown` → 503, never 404), and the joined path goes through the SAME `resolveServableAttachmentPath` as an attachment by id (symlink re-resolution, remote re-probe, guard), then `folderAllowedForUser` once more on the resolved file, before `serveServableRaw` (the attachment raw route's body, shared) streams it. So browser requests still never carry a path. ⚠️ Grants live in their own registry (`folderGrants`, 32 per session, cleared with the session's attachments), NOT the attachment registry: that one is capped at 200 per session, and paging a folder of 300 renders would evict the session's real attachments. ⚠️ A local folder is never touched unbounded (#516 rule): a folder on a network mount that stopped answering answers 503 with `describeUnknownPath()`, not 404 and not a frozen server. ⚠️ The remote listing script tells "missing" (`E|n`, 404) from "is a file" (`E|f`, 400 `Not a folder`), because the client falls back to the file preview on `Not a folder`; a remote extensionless file otherwise answered "Folder not found". ⚠️ `.folder-grid-overlay` sits at `z-index: 5090`, one step BELOW the preview (5100) and above the response viewer (5000): a tile's preview opens on top and closing it lands back on the grid. ⚠️ ←/→/Esc are handled in a document CAPTURE listener with `stopPropagation`, because the terminal keeps keyboard focus under the overlays and an arrow that reached xterm would be typed into the session; inputs other than xterm's helper textarea keep their keys. Tests: `test/routes/folder-grid-routes.test.ts` (incl. the listing script on a real `sh`), `test/folder-grid-ui.test.ts`.
+**Folder grid: a folder is granted, then served by bare file name.** A folder path (rooted or `~/` whose last segment has no extension, relative only with a trailing `/`; `FOLDER_PATH_LINK_PATTERN` + `folderLinkPath()`) opens `openFolderGrid()` (panels-ui.js), as does the preview's "Show folder" button. `POST /api/sessions/:id/folders {path}` (`src/folder-listing.ts`) resolves the folder (locally a bounded `probePathKind(…, { pastCap: true })` first, then async `fs.realpath`; remotely one ssh round trip via `remoteListFolder`, through `runWithRemoteSshLimit`), runs the attachment guard on it (blocklist, `confineToWorkspace`, and in multi-user mode `folderAllowedForUser`: a non-admin only inside their own `userSpacePath` or the session's `workingDir`, as the filesystem path picker), locally BEFORE reading it, lists non-hidden subfolders and files of a supported attachment type (each file also blocklist-checked, newest first, capped at `MAX_FOLDER_ENTRIES`), and GRANTS it an id. Files are then fetched as `GET …/folders/:folderId/files/:name/(raw|preview|thumbnail)`: `:name` must be a bare file name of a supported type (no `/`, `\`, NUL, no leading `.`, since the listing hides those), the local file is probed bounded (`unknown` → 503, never 404), and the joined path goes through the SAME `resolveServableAttachmentPath` as an attachment by id (symlink re-resolution, remote re-probe, guard), then the same gate registration applies to what a symlink RESOLVES to (a supported extension on the resolved path and a regular file: locally `fs.stat`, remotely the probe kind; else 400, so `shot.png -> ../secret.bin` is not served and a FIFO or device behind a supported name never reaches `open`), then `folderAllowedForUser` once more on the resolved file, before `serveServableRaw` (the attachment raw route's body, shared) streams it. So browser requests still never carry a path. ⚠️ Grants live in their own registry (`folderGrants`, 32 per session, cleared with the session's attachments), NOT the attachment registry: that one is capped at 200 per session, and paging a folder of 300 renders would evict the session's real attachments. ⚠️ A local folder is never touched unbounded (#516 rule): a folder on a network mount that stopped answering answers 503 with `describeUnknownPath()`, not 404 and not a frozen server. ⚠️ The remote listing script tells "missing" (`E|n`, 404) from "is a file" (`E|f`, 400 `Not a folder`), because the client falls back to the file preview on `Not a folder`; a remote extensionless file otherwise answered "Folder not found". ⚠️ `.folder-grid-overlay` sits at `z-index: 5090`, one step BELOW the preview (5100) and above the response viewer (5000): a tile's preview opens on top and closing it lands back on the grid. ⚠️ ←/→/Esc are handled in a document CAPTURE listener with `stopPropagation`, because the terminal keeps keyboard focus under the overlays and an arrow that reached xterm would be typed into the session; inputs other than xterm's helper textarea keep their keys. ⚠️ A route PARAMETER is capped by the router (Fastify's default is 100 characters, answered as 404 "Route not found"), and a file name goes up to 255, percent-encoded: the server sets `routerOptions.maxParamLength` to `MAX_ROUTE_PARAM_LENGTH` (route-helpers.ts), the route test harness uses the same constant, and a wiring guard pins it. ⚠️ `~/` in a Docker case is refused with 400 (attachment POST and `POST …/folders`): the session is local for these routes, but `~` inside the container is the container's own home, and expanding it on the host would open a different file than the one the agent printed. Tests: `test/routes/folder-grid-routes.test.ts` (incl. the listing script on a real `sh`), `test/folder-grid-ui.test.ts`.
 
 **Text reuses the edit-mode allowlist; markup stays download-only.** `TEXT_ATTACHMENT_EXTENSIONS` IS `EDITABLE_EXTENSIONS` (`config/file-editing.ts`) rather than a second curated list that would drift from it: if the viewer would open a file for editing inside the workspace, the same file outside it can be read. The justification for widening is that the agent in the session can already `cat` any of these and the picker already previews them, so the suffix was never the confidentiality gate; the path guard is (sensitive-file blocklist, `/root` and `/etc` trees, realpath first). ⚠️ Two consequences had to be handled at the same time: `~/.codeman*/state.json` joined `isSensitivePath` (it persists `SessionState.envOverrides`, and the env allowlist admits key-shaped names like `GEMINI_API_KEY`, so it can hold a live credential), and `html`/`htm` joined `svg` in `serveRawFile`'s **download-only** branch so that widening what can be READ never widens what can RUN on our own origin. Text with no dedicated MIME entry goes out as inert `text/plain; charset=utf-8` + `nosniff`, matching the picker. The by-id text preview is bounded like the workspace one: a `Range` request for the first 512KB (a real partial read, not a discarded 50MB download) plus a 500-line cap, with the footer saying so.
 

docs/security-architecture.md

@@ -382,6 +382,9 @@ left out). The grant is an id for a resolved folder; files are served by
 `folderId` + a bare file name only (no `/`, `..` or NUL, supported type), and each
 request re‑runs `resolveServableAttachmentPath` on the joined path, so a file that
 was swapped for a symlink to a blocked target after listing is still refused.
+The file a symlink resolves to is held to the attachment gate as well (supported
+extension, regular file), so a supported-looking name cannot serve an arbitrary
+file, and a FIFO or device node is never opened.
 In multi‑user mode a regular user is held to the filesystem path picker's rule
 (`folderAllowedForUser`): the folder, and again each served file after symlink
 resolution, must sit inside their own `userSpacePath` or the session's

src/web/routes/file-routes.ts

@@ -564,8 +564,20 @@ function getKnownSessionWorkingDir(
 interface SessionFileScope {
   workingDir: string;
   remote?: SessionRemote;
+  /** The session runs inside a Docker case: a local session for these routes, but `~` is the container's. */
+  docker?: boolean;
 }
 
+/**
+ * A Docker case is a LOCAL session for the file routes (the workspace is a
+ * bind mount, so its paths are host paths), but `~` inside the container is the
+ * container's own seeded home, not this host's. Expanding `~/x.png` against the
+ * host's home would open a different file than the one the agent printed, so
+ * the form is refused instead of guessed.
+ */
+const DOCKER_HOME_PATH_ERROR =
+  'A ~/ path inside a Docker case is the container home, which this server cannot read; use the absolute path';
+
 /**
  * The file-access scope of a session, live or persisted — the `workingDir`-only
  * variant of {@link getKnownSessionWorkingDir}, plus the remote metadata the routes
@@ -583,12 +595,12 @@ function getKnownSessionFileScope(
   const user = getAuthUser(req);
   const liveSession = ctx.sessions.get(sessionId);
   if (liveSession && canAccessOwned(user, liveSession.owner)) {
-    return { workingDir: liveSession.workingDir, remote: liveSession.remote };
+    return { workingDir: liveSession.workingDir, remote: liveSession.remote, docker: !!liveSession.docker };
   }
 
   const stored = ctx.store.getSession(sessionId);
   if (stored && canAccessOwned(user, (stored as { owner?: string }).owner)) {
-    return { workingDir: stored.workingDir, remote: stored.remote };
+    return { workingDir: stored.workingDir, remote: stored.remote, docker: !!stored.docker };
   }
 
   reply.code(404).send(createErrorResponse(ApiErrorCode.NOT_FOUND, `Session ${sessionId} not found`));
@@ -2187,6 +2199,10 @@ export function registerFileRoutes(app: FastifyInstance, ctx: SessionPort & Even
       reply.code(400).send(createErrorResponse(ApiErrorCode.INVALID_INPUT, 'Missing attachment path'));
       return;
     }
+    if (session.docker && body.path.startsWith('~/')) {
+      reply.code(400).send(createErrorResponse(ApiErrorCode.INVALID_INPUT, DOCKER_HOME_PATH_ERROR));
+      return;
+    }
 
     try {
       // A remote case registers a path that lives on the REMOTE host: the guard and
@@ -2388,6 +2404,10 @@ export function registerFileRoutes(app: FastifyInstance, ctx: SessionPort & Even
       reply.code(400).send(createErrorResponse(ApiErrorCode.INVALID_INPUT, 'Missing folder path'));
       return;
     }
+    if (scope.docker && body.path.startsWith('~/')) {
+      reply.code(400).send(createErrorResponse(ApiErrorCode.INVALID_INPUT, DOCKER_HOME_PATH_ERROR));
+      return;
+    }
     try {
       const listing = await listFolder(id, body.path, {
         sessionWorkingDir: scope.workingDir,

test/routes/folder-grid-routes.test.ts

@@ -320,6 +320,46 @@ describe('folder grid routes — local folder', () => {
     expect(res.body).toBe('long-png');
   });
 
+  // A Docker case is a LOCAL session for the file routes, but its `~` is the
+  // container's home: a separate, seeded directory. `~/x.png` printed inside the
+  // container used to open the HOST's `~/x.png`.
+  describe('~/ in a Docker case', () => {
+    beforeEach(() => {
+      (harness.ctx._session as { docker?: unknown }).docker = {
+        hostId: 'local',
+        label: 'local',
+        engine: 'docker',
+        image: 'codeman-sandbox',
+        containerName: 'codeman-case-test',
+        hostWorkspacePath: root,
+        containerWorkdir: root,
+        network: 'bridge',
+      };
+    });
+
+    it('refuses a ~/ folder, and still lists an absolute one', async () => {
+      const home = await grant('~/renders');
+      expect(home.statusCode).toBe(400);
+      expect(JSON.parse(home.body).error).toMatch(/docker/i);
+      expect((await grant(dir)).statusCode).toBe(200);
+    });
+
+    it('refuses a ~/ attachment, and still registers an absolute one', async () => {
+      const post = (path: string) =>
+        harness.app.inject({ method: 'POST', url: `/api/sessions/${sessionId}/attachments`, payload: { path } });
+      const home = await post('~/renders/old.png');
+      expect(home.statusCode).toBe(400);
+      expect(JSON.parse(home.body).error).toMatch(/docker/i);
+      expect((await post(join(dir, 'old.png'))).statusCode).toBe(200);
+    });
+  });
+
+  it('keeps resolving ~/ for a session that is not in a Docker case', async () => {
+    // The contrast: only the Docker case is turned away, `~/` itself still works.
+    const res = await grant('~/this-folder-does-not-exist-codeman-test');
+    expect(res.statusCode).toBe(404);
+  });
+
   it('404s an unknown folder id and another session’s grant', async () => {
     const res = await harness.app.inject({
       method: 'GET',