fix(preview): folder grid review — multi-user scope, bounded probing, smaller items

- Multi-user: a non-admin's folder must resolve inside their own userSpacePath
  or the session's workingDir (folderAllowedForUser, the path picker's rule),
  checked on the resolved folder before it is read and again on each served
  file after symlink resolution; 403 otherwise.
- listFolder probes the local folder with probePathKind({ pastCap: true })
  first (unknown -> 503 via describeUnknownPath, never 404), then async
  fs.realpath; resolveFolderFile uses probePathKind instead of fs.stat.
- The guard runs on the realpath before readdir.
- FOLDER_PATH_LINK_PATTERN ends a folder at ':' (quadratic `://` rescan on
  colon runs; PATH=/a:/b linked as one folder).
- Load counters drop stale preview / folder-grid responses; closing the grid
  invalidates a listing still in flight.
- validFolderFileName refuses a leading dot; the remote listing matches
  extensions in any case.
- Docs: folder grid in the z-index lists; multi-user rule and bounded probe in
  the invariants and security docs.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -375,7 +375,7 @@ A file path an agent prints is a link on both surfaces it can appear on, and cli
 
 **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`.
 
-**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 `realpath`; remotely one ssh round trip via `remoteListFolder`, through `runWithRemoteSshLimit`), runs the attachment guard on it (blocklist, `confineToWorkspace`), 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), and the joined path goes through the SAME `resolveServableAttachmentPath` as an attachment by id (symlink re-resolution, remote re-probe, guard) 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. ⚠️ 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 `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`.
 
 **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.
 
@@ -1063,7 +1063,7 @@ Tests: `test/mobile-prompt-composer.test.ts` (in the CI gate, deliberately not u
 
 ### Z-index layers
 
-**Z-index layers**: subagent windows (1000), split picker menu (1000, `.split-picker-menu`), Tiles count menu (1000, `.tile-count-menu`), the closing grid's still copy (`.tile-grid-ghosts`, z-index 3 inside `.main`, over the single view coming back; hidden under `.main.webview-active`), plan agents (1100), mobile/tablet fixed header (1200, `mobile.css`), modals on ≤768px (1300 — must beat the fixed header or the modal close button is buried), log viewers (2000), connection-loss overlay (2500, above the fixed header and modals), image popups (3000), response viewer (5000, backdrop 4999), file-preview overlay (5100 — must outrank the response viewer, which can launch it; at its old 2000 a path clicked in the chat opened BEHIND the chat), toasts/path picker (10000+, deliberately above the preview), the custom-model center-status banner (10001, `.center-status-banner` — `[hidden]` must re-assert `display: none` over its own `display: flex`, same trap as `.home-sessions[hidden]`, or `dismiss()` leaves an invisible click-blocker dead centre on screen), the swap-confirm and context-warning modals (10010, `#customModelSwapConfirmModal`/`#customModelContextWarningModal` — must clear both the plain `.modal` z-index of 1000 and the center-status banner it can appear over), terminal touch-selection bar (900 — above terminal content and the local-echo overlay, deliberately BELOW floating agent windows so it can never cover their controls), local echo overlay (7), iOS IME composition preview (EFFECTIVE layer depends on its home: with local echo on it is part of the local echo overlay at 7, drawn by `setComposition()` as an underlined tail after the pending text; with local echo off it is a span at z-index 6 inside `.xterm-helpers`, but `.xterm-helpers` is its own z-index 5 stacking context, so the span's effective layer is 5. That is below the overlay's 7, which is why the span cannot be used while the overlay holds text: typed text never reaches the PTY before Enter, the PTY cursor that places the span stays at the prompt start, and the overlay's opaque line div covers it).
+**Z-index layers**: subagent windows (1000), split picker menu (1000, `.split-picker-menu`), Tiles count menu (1000, `.tile-count-menu`), the closing grid's still copy (`.tile-grid-ghosts`, z-index 3 inside `.main`, over the single view coming back; hidden under `.main.webview-active`), plan agents (1100), mobile/tablet fixed header (1200, `mobile.css`), modals on ≤768px (1300 — must beat the fixed header or the modal close button is buried), log viewers (2000), connection-loss overlay (2500, above the fixed header and modals), image popups (3000), response viewer (5000, backdrop 4999), folder grid (5090, `#folderGridOverlay` — above the response viewer a folder link opens it from, below the file preview its tiles open, so a tile's preview and its ←/→ paging sit on top of the grid), file-preview overlay (5100 — must outrank the response viewer, which can launch it; at its old 2000 a path clicked in the chat opened BEHIND the chat), toasts/path picker (10000+, deliberately above the preview), the custom-model center-status banner (10001, `.center-status-banner` — `[hidden]` must re-assert `display: none` over its own `display: flex`, same trap as `.home-sessions[hidden]`, or `dismiss()` leaves an invisible click-blocker dead centre on screen), the swap-confirm and context-warning modals (10010, `#customModelSwapConfirmModal`/`#customModelContextWarningModal` — must clear both the plain `.modal` z-index of 1000 and the center-status banner it can appear over), terminal touch-selection bar (900 — above terminal content and the local-echo overlay, deliberately BELOW floating agent windows so it can never cover their controls), local echo overlay (7), iOS IME composition preview (EFFECTIVE layer depends on its home: with local echo on it is part of the local echo overlay at 7, drawn by `setComposition()` as an underlined tail after the pending text; with local echo off it is a span at z-index 6 inside `.xterm-helpers`, but `.xterm-helpers` is its own z-index 5 stacking context, so the span's effective layer is 5. That is below the overlay's 7, which is why the span cannot be used while the overlay holds text: typed text never reaches the PTY before Enter, the PTY cursor that places the span stays at the prompt start, and the overlay's opaque line div covers it).
 
 ## Security layers