fix(uploads): bound the paste-image workspace probe (#516)

The paste-image route wrote under session.workingDir via ensureUploadDir
with no bounded probe, so an upload onto a stalled network mount held one
of libuv's few threadpool workers until the mount answered. Probe the
workspace with probePathKind past the stall cap before the first disk
touch and refuse an unknown mount through describeUnknownPath, the way
POST /api/sessions already does.

docs/architecture-invariants.md

@@ -1085,7 +1085,7 @@ Tests: `test/mobile-prompt-composer.test.ts` (in the CI gate, deliberately not u
 
 Target: 20 sessions, 50 agent windows at 60fps. Limits in `src/config/`: terminal 32MB (see below), text 1MB, messages 1000, max agents 500, max sessions 50, max SSE clients 100. **Terminal history** (`src/config/terminal-history.ts`, COD-80): tmux history-limit 100k lines, PTY buffer 32MB max / 24MB trim (env `CODEMAN_MAX_TERMINAL_BUFFER`/`CODEMAN_TRIM_TERMINAL_TO`; the env-derived trim is clamped ≤75% of max — trim ≥ max would disable `BufferAccumulator` trimming entirely = unbounded memory); browser xterm scrollback stays a separate hardcoded 50k (`DEFAULT_SCROLLBACK` in constants.js — 100k/tab is a mobile-memory hazard). tmux <3.7 allocates history at pane creation, so `createSession()` sets the global default in the same command queue immediately before `new-session`; tmux 3.7+ instead creates the session and targets only that pane, because changing the global option can resize and trim unrelated live panes. A settings change resizes tracked panes only on 3.7+ and otherwise affects future panes; no version can recover lines already evicted. Settings keys `terminalScrollbackLines`/`terminalBufferMaxBytes`/`terminalBufferTrimBytes` are schema-validated but inert (only `tmuxHistoryLimit` is wired); `buffer-limits.ts` re-exports the defaults. Text/message limits are env-overridable too (`CODEMAN_MAX_TEXT_OUTPUT`/`CODEMAN_TRIM_TEXT_TO`/`CODEMAN_MAX_MESSAGES`). **Image upload** (`image-input.js` / `config/buffer-limits.ts`): up to `_maxBatchImages` 20 images/batch (bounded concurrency 3), per-file `MAX_PASTE_IMAGE_BYTES` 50MB (env `CODEMAN_MAX_PASTE_IMAGE_BYTES`); the mobile camera-roll picker auto-downscales to fit before upload. **HEIC paste uploads** (#151): converted server-side to JPEG in a `worker_threads` worker (`web/heic-jpeg-worker.ts`, resourceLimits + 30s timeout) gated by `runWithConversionLimit()`; detection is magic-byte based (covers Android/MIUI HEIFs mislabeled as JPEG); headers declaring > 64MP are rejected 415 BEFORE decode (decompression-bomb guard). Deps: `heic-decode` + `jpeg-js`. Use `LRUMap` for bounded caches, `StaleExpirationMap` for TTL cleanup. Anti-flicker pipeline: `docs/terminal-anti-flicker.md`.
 
-**Prompt uploads live in `<workspace>/.codeman-uploads/`** (`POST /api/sessions/:id/paste-image`; the names live ONLY in `src/web/paste-image-gc.ts`): IN the workspace because that is the only path that resolves identically for a local agent and a container (only the workspace is bind-mounted, at the same absolute path; `~/.codeman` is not); hidden so it stays out of `git status` and the agent's view of the repository; FLAT because a nested `<workspace>/.codeman/` IS the data dir (`join(homedir(), '.codeman')`, `src/config/instance.ts`) when the workspace is the home directory, which nothing refuses; and self-ignoring through a `.gitignore` of `*` written once with `wx`, so a file already there is the user's and stays. The pre-move `.claude-images/` receives nothing but stays readable for one release: `UPLOAD_DIR_NAMES` lists both, the hourly sweep and the delete cleanup in `cleanupSession()` go through `uploadDirs()`, and the image watcher's ignore filter reads the names. ⚠️ `uploadDirs()` is async: the working directory is a user-chosen path, so it is probed BOUNDED first (`probePathKind()`, the #516 rule; `unknown` is skipped and never touched, the hourly sweep keeps the stall cap and `cleanupSession()` passes `pastCap`, since it acts on one path at the user's request), and the lstat and realpath after it are `fs.promises` calls, never sync, because the sweep runs 30 s after boot and hourly over every live session and a linked case on a dead mount would otherwise freeze the whole server. It returns only REAL directories (lstat at the leaf, so a planted `.codeman-uploads -> /other-case/.codeman-uploads` is never listed: `readdir` follows a link to a directory, and the sweep would otherwise age out the other case's uploads through it), none that is or contains `getDataDir()` (contrived, `CODEMAN_INSTANCE=uploads` makes `~/.codeman-uploads` the data dir of a home workspace and `CODEMAN_DATA_DIR` can point inside one, but it is one check next to a recursive delete; one strictly INSIDE the data dir is listed, since it only ever holds uploads and a workspace like the `~/.codeman/app` that `install.sh` clones would otherwise never have its uploads collected), and nothing for a remote (SSH) session, whose `workingDir` is the remote path and would otherwise name a same-named LOCAL directory for the sweep and the delete. The check is made when the directories are listed: a same-user process that swaps a listed directory for a link during the sweep's awaits is accepted (Node has no `openat()`, and that actor already writes anywhere this process can). The route refuses a remote (SSH) session with 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. Tests: `test/paste-image-gc.test.ts`, `test/paste-image-dir-shared.test.ts`, the paste-image block of `test/routes/session-routes.test.ts`.
+**Prompt uploads live in `<workspace>/.codeman-uploads/`** (`POST /api/sessions/:id/paste-image`; the names live ONLY in `src/web/paste-image-gc.ts`): IN the workspace because that is the only path that resolves identically for a local agent and a container (only the workspace is bind-mounted, at the same absolute path; `~/.codeman` is not); hidden so it stays out of `git status` and the agent's view of the repository; FLAT because a nested `<workspace>/.codeman/` IS the data dir (`join(homedir(), '.codeman')`, `src/config/instance.ts`) when the workspace is the home directory, which nothing refuses; and self-ignoring through a `.gitignore` of `*` written once with `wx`, so a file already there is the user's and stays. The pre-move `.claude-images/` receives nothing but stays readable for one release: `UPLOAD_DIR_NAMES` lists both, the hourly sweep and the delete cleanup in `cleanupSession()` go through `uploadDirs()`, and the image watcher's ignore filter reads the names. ⚠️ `uploadDirs()` is async: the working directory is a user-chosen path, so it is probed BOUNDED first (`probePathKind()`, the #516 rule; `unknown` is skipped and never touched, the hourly sweep keeps the stall cap and `cleanupSession()` passes `pastCap`, since it acts on one path at the user's request), and the lstat and realpath after it are `fs.promises` calls, never sync, because the sweep runs 30 s after boot and hourly over every live session and a linked case on a dead mount would otherwise freeze the whole server. It returns only REAL directories (lstat at the leaf, so a planted `.codeman-uploads -> /other-case/.codeman-uploads` is never listed: `readdir` follows a link to a directory, and the sweep would otherwise age out the other case's uploads through it), none that is or contains `getDataDir()` (contrived, `CODEMAN_INSTANCE=uploads` makes `~/.codeman-uploads` the data dir of a home workspace and `CODEMAN_DATA_DIR` can point inside one, but it is one check next to a recursive delete; one strictly INSIDE the data dir is listed, since it only ever holds uploads and a workspace like the `~/.codeman/app` that `install.sh` clones would otherwise never have its uploads collected), and nothing for a remote (SSH) session, whose `workingDir` is the remote path and would otherwise name a same-named LOCAL directory for the sweep and the delete. The check is made when the directories are listed: a same-user process that swaps a listed directory for a link during the sweep's awaits is accepted (Node has no `openat()`, and that actor already writes anywhere this process can). The route refuses a remote (SSH) session with 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. ⚠️ And because a live session's workspace can go onto a network mount that later stops answering, the route probes `session.workingDir` BOUNDED (`probePathKind(..., { pastCap: true })`) before the first disk touch, refusing an `unknown` mount through `describeUnknownPath()` (OPERATION_FAILED) exactly as `POST /api/sessions` does, so a mount already unreachable cannot freeze a libuv worker on every upload (`ensureUploadDir()`'s own lstat/mkdir then start on a reachable path; a mount that dies between the probe and that write is the same residual race `POST /api/sessions` accepts, since a pre-check cannot bound the write that follows it). Tests: `test/paste-image-gc.test.ts`, `test/paste-image-dir-shared.test.ts`, the paste-image block of `test/routes/session-routes.test.ts`, `test/routes/session-create-unreachable-path.test.ts`.
 
 ### Process-tree walks are bounded