feat(lanes): split panes on one lane, in-place file editing, hunk review bar

- Split view: every pane shows the selected lane, each in its own tmux
  session (`slot` 0-3 on POST /api/lanes/:id/start; slot 0 stays the
  lane's `run_id`, slots 1-3 are `agenthub-lane-<id>-<slot>`). A pane's
  Active runs hides what the other panes show; stop/reset/remove kill
  every slot. No per-pane lane picker any more.
- Whole-file editor: PUT /api/lanes/:id/git/file (lane-file-write.js)
  with the read path's guards, existing text files only, and a baseSha
  stale check (409 ESTALE). A file it cannot take says why.
- Per-hunk review bar under each hunk's last changed line: prev/next,
  "n of N", Undo, Keep. Review diffs no longer nest their own scroll box
  (unless windowed), so navigation moves the one real scroller.
- Files tree lists untracked-not-ignored files and colours entries by git
  status (M/U/A/D/R), folders holding changes get a dot.
- Changes panel: Unstage all on the single commit/Stage-all row; sizes
  Narrow (30%) / Medium / Full screen, no 70/30.
- Lane card: the needs-you banner is gone (the strip tile keeps it).

docs/API.md

@@ -261,6 +261,8 @@ All fields are optional. The tool (CLI invoked) comes from the lane itself, neve
 - **`approval`** — one of `on-request` or `never`, or omitted/empty for no approval prompt. Passed to `codex -a <value>`.
 - **`resumeSessionId`** or **`resumeLast: true`** — resume an earlier run instead of starting new. For Codex lanes specifically, `resumeLast: true` uses `codex resume --last`; `resumeSessionId` uses `codex resume <sessionId>`. For Claude lanes, `resumeSessionId` re-attaches a Claude session by id.
 
+- **`slot`** — which Workspace split pane's session to start, `0`–`3` (default `0`, else `400 EBADSLOT`). Slot 0 is the lane's own `agenthub-lane-<id>` and is what `run_id` records; slots 1–3 are extra sessions on the same lane, `agenthub-lane-<id>-<slot>`, and never touch `run_id`/`status`. The response adds `run_id`: the session this start opened. `stop`, `reset` and `remove` kill every slot's session, not only `run_id`.
+
 Error `503 ETMUXMISSING` is returned when the host has no `tmux` binary. Every run the dashboard starts is a tmux session, so this is a missing dependency rather than a bad request — the message carries the install command, and the same code comes back from `POST /api/run`. Nothing else in the dashboard is affected.
 
 Error `409 ERUNLIVE` is returned if the lane already has a live run; stop it first with the `stop` action. The same code and status come back when the lane's tmux pane is already running an agent while a `prompt` or `resumeSessionId` was sent — that argv cannot be typed over a live agent, so the request is refused instead of answered 200 with nothing done. A start that asks for neither still adopts the existing pane silently.
@@ -496,6 +498,7 @@ that file.
 ```http
 GET /api/lanes/:id/git/log?limit=30[&file=<path>]
 GET /api/lanes/:id/git/file?path=<path>[&rev=work|HEAD|<sha>]
+PUT /api/lanes/:id/git/file   {path, content, baseSha}
 GET /api/lanes/:id/git/ls?q=<substring>
 GET /api/lanes/:id/git/tree?path=<dir>
 GET /api/lanes/:id/git/tree-all
@@ -510,7 +513,15 @@ and file explorer. All four are read-only and unguarded, and all four answer
   commits touching that path — relative, no `..` segment, else
   `400 EBADPATH`. Reading one commit's diff is
   `/git/changes?range=commit&sha=`.
-- **`/git/file`** → `{available, path, rev, binary, truncated, lines}`.
+- **`PUT /git/file`** saves the whole-file editor (same-origin guarded;
+  `server/lib/lane-file-write.js`). Same path guards as the read, plus: the
+  file must already exist, be text and within the 1 MB cap, and `baseSha`
+  must equal the `sha` it was opened at — otherwise `409 ESTALE`, never an
+  overwrite. `403 ESECRET` for `settings.local.json`; `400 EBADPATH`,
+  `ENOFILE`, `EBADCONTENT`, `ETOOBIG`, `EBINARY`. Answers the file re-read,
+  fresh `sha` included. CRLF endings and the final newline are preserved.
+- **`/git/file`** → `{available, path, rev, binary, truncated, lines, sha?}`
+  (`sha` only for a whole, textual `work` file: what a save sends back).
   `rev=work` (default) is the file on disk — the one branch that reads the
   filesystem, and it is realpath-confined to the lane directory (a symlink
   resolving outside it is `EBADPATH`); anything else goes through
@@ -530,10 +541,12 @@ and file explorer. All four are read-only and unguarded, and all four answer
 - **`/git/ls`** → `{available, paths, truncated, total}`, capped at 500. It
   reads `git ls-files`, so ignored files never appear and no skip-list has to
   be maintained; basename hits rank first.
-- **`/git/tree`** → `{available, path, entries:[{name, path, dir}], truncated}`
-  — one directory level, tracked entries only, directories folded and listed
-  first. `400 EBADPATH` for a path that escapes the lane.
-- **`/git/tree-all`** → `{available, levels: {"<dir>": [{name, path, dir}]}, truncated}` — every level of the tracked tree from ONE `git ls-files`, each level shaped and capped like `/git/tree`'s; the Files tab's **Expand all folders** is this one request instead of one per folder.
+- **`/git/tree`** → `{available, path, entries:[{name, path, dir, status?, changed?}], truncated}`
+  — one directory level: tracked files plus untracked ones git does not
+  ignore (`ls-files --cached --others --exclude-standard`), directories folded
+  and listed first. A changed file carries its porcelain `status` (` M`, `??`,
+  `A `, ` D`…), a folder with anything changed under it `changed: true`. `400 EBADPATH` for a path that escapes the lane.
+- **`/git/tree-all`** → `{available, levels: {"<dir>": [{name, path, dir}]}, truncated}` — every level of the same tree (entries decorated the same way) from ONE `git ls-files`, each level shaped and capped like `/git/tree`'s; the Files tab's **Expand all folders** is this one request instead of one per folder.
 
 #### Read a lane's own branches
 

docs/LANES.md

@@ -421,14 +421,14 @@ The dashboard web UI merges lanes and runs into a single **Workspace** page acce
 - **Detail panel** — the selected lane's declared stage, its inferred stage when detection leads, a full-width pipeline map, and a legend naming all five node states plus the dashed-amber inferred treatment.
 - **Terminal** — a real interactive terminal (xterm.js) displaying the tmux session's PTY output, with full support for interactive commands, editors, and pagers. A live run keeps its rendered history and scroll position when scrolling. It grabs the keyboard the moment it appears, so typing goes into the pane without clicking it first, and when the pane's process ends — a double Ctrl+C out of `claude`, `exit`, a crash — the console returns to the run setup form on its own, with no "New run" click.
 - **Clipboard in a pane** — the lane's tmux session is started with the graphical session's own `DISPLAY`/`WAYLAND_DISPLAY`/`XAUTHORITY`/`XDG_RUNTIME_DIR` (read from `systemctl --user show-environment`, this process's own values winning; `server/lib/desktop-env.js`). The dashboard normally runs as a systemd *user* service, which has none of them, so a pane it started had no clipboard at all and `claude` answered "no image found in clipboard" on every image paste while the same CLI pasted fine in a terminal. Only those four names are forwarded, and only into panes this dashboard spawns — an already-running pane keeps the environment it was started with, so it needs a restart to gain one.
-- **Split view** — a layout toggle (one pane / two side by side / a 2×2 grid, drawn as icons rather than the words, with the count kept as each button's `aria-label` and tooltip) renders that many independent terminal panes side by side (`grid-cols-2` for 2, a 2×2 grid for 4). Layout 1 is bound to the lane strip's selection, same as always; layouts 2 and 4 give each pane its own lane picker, independent of the strip. The chosen layout and each pane's lane persist to `localStorage` (`agenthub.workspace.splitView`) across reloads.
-- **Lane grid** — one card per lane, 1 column, 2 at `md`, 3 at `xl`. Each card carries the lane id, liveness dot and status, title, declared stage and time-on-stage, the `auto:` chip when detection leads, the kind and CI tags, the working-copy facts from `GET /api/lanes/:id/git`, the needs-you banner, and the action row.
+- **Split view** — a layout toggle (one pane / two side by side / a 2×2 grid, drawn as icons rather than the words, with the count kept as each button's `aria-label` and tooltip) renders that many terminal panes side by side (`grid-cols-2` for 2, a 2×2 grid for 4). EVERY pane is bound to the lane strip's selection — there is no per-pane lane picker — and each pane owns its own tmux session on that lane: pane 0 is the lane's `agenthub-lane-<id>` (its `run_id`), panes 1–3 are `agenthub-lane-<id>-<slot>` (`POST /api/lanes/:id/start` with `slot`). A pane's **Active runs** leaves out the runs the other panes are showing, so one terminal is never attached twice side by side. Only the layout persists to `localStorage` (`agenthub.workspace.splitView`); a stored per-pane lane id from an older build is ignored.
+- **Lane grid** — one card per lane, 1 column, 2 at `md`, 3 at `xl`. Each card carries the lane id, liveness dot and status, title, declared stage and time-on-stage, the `auto:` chip when detection leads, the kind and CI tags, the working-copy facts from `GET /api/lanes/:id/git`, and the action row. The needs-you message (`needs_action`) is on the lane strip tile only — the detail card no longer repeats it as a banner.
 
 Run history is per lane, queryable via `GET /api/run/history?laneId=<n>`.
 
-**A console pane follows the lane it shows.** Selecting another lane — from the lane strip in layout 1, or from a pane's own lane picker in layouts 2 and 4 — swaps that pane's cwd, run history and terminal over to the new lane. If the new lane already has a live run in `GET /api/run`, the pane re-attaches to it immediately, so each lane sticks to its own `agenthub-lane-<id>` tmux session; if it has none, the pane shows that lane's setup form. Nothing of the previous lane (a half-typed prompt, its terminal) carries over.
+**A console pane follows the lane it shows.** Selecting another lane on the lane strip swaps every pane's cwd, run history and terminal over to the new lane. If the new lane already has a live session for that pane's slot in `GET /api/run`, the pane re-attaches to it immediately, so each pane sticks to its own `agenthub-lane-<id>[-<slot>]` tmux session; if it has none, the pane shows that lane's setup form. Nothing of the previous lane (a half-typed prompt, its terminal) carries over.
 
-The **working directory** field tracks the selected lane's own `cwd` specifically, and re-syncs as soon as that path is known rather than only when the selection changes — a pane can render before `GET /api/lanes` has answered (split view restores its pane lanes from `localStorage`), and its lane id never changes afterwards. `RunSetup` submits that string verbatim to `POST /api/lanes/:id/start`, so a cwd left over from the previous lane or from the home default would start the run in the wrong folder. The home suggestion is used only while no lane is selected at all.
+The **working directory** field tracks the selected lane's own `cwd` specifically, and re-syncs as soon as that path is known rather than only when the selection changes — a pane can render before `GET /api/lanes` has answered (the lane list loads after the page mounts), and its lane id never changes afterwards. `RunSetup` submits that string verbatim to `POST /api/lanes/:id/start`, so a cwd left over from the previous lane or from the home default would start the run in the wrong folder. The home suggestion is used only while no lane is selected at all.
 
 **Picking a session to resume starts it right away.** In the setup form's Fresh/Resume switch, choosing a session from the resume picker fires the start immediately — `POST /api/lanes/:id/start` with that `resumeSessionId` and the session's own `cwd` — and the pane switches straight to the terminal. A resume carries its own transcript, so there is nothing to type first: the prompt box stays optional for resumes (the Run button no longer requires it) and required for fresh runs. A resume also **sends no prompt at all** — whatever is left in that box is dropped rather than fired as an extra turn into the session being continued. Type into the tmux terminal once it's attached.
 
@@ -575,9 +575,9 @@ says more than any sentence the dashboard could write.
 
 To the right of the lane detail sits a collapsible **Changes** card (its state
 persists per viewer in `localStorage`). Its header holds **one** control, which
-steps narrow → 50/50 → 70/30 → full width (the console beside it is hidden, never unmounted) → closed (`agenthub.workspace.changesSize`
+steps **Narrow** (30%) → **Medium** (50/50) → **Full screen** (the console beside it is hidden, never unmounted) → closed (`agenthub.workspace.changesSize`
 alongside `agenthub.workspace.changesOpen`); the collapsed rail reopens it
-narrow. Reading a diff and watching a console want opposite amounts of room and
+narrow. A stored size from an older build that no longer exists (`wide`) falls back to narrow. Reading a diff and watching a console want opposite amounts of room and
 which one is "work" changes several times an hour, so the width is a step, not
 a setting — and one button beats a width button wedged beside a collapse button
 in the panel's tightest corner. It is icon-only, and the icon it draws is the
@@ -591,7 +591,18 @@ only one that answers "show me the code" rather than "show me the change"):
   them — a folder's children render nested under it, siblings stay visible,
   and a toolbar button expands or collapses every folder at once (each
   unfetched level lazily calls `/git/tree` the first time it's opened).
-  Opening a file entry shows the whole file (`/git/file`).
+  Untracked files git does not ignore are listed too, and the tree is
+  decorated like VS Code's: a modified file is amber with `M`, an untracked
+  one green with `U` (`A` added, `D` deleted and struck through, `R`
+  renamed), and a folder holding any of them gets an amber dot. The colours
+  come with the tree read, so **Refresh** re-reads them.
+  Opening a file entry shows the whole file (`/git/file`). Its **Edit** button
+  (any range but a commit) turns that view into a text editor: **Save** (or
+  Ctrl/Cmd+S) is `PUT /api/lanes/:id/git/file`, which writes only over the
+  exact version that was opened — a file the agent changed meanwhile answers
+  `409 ESTALE` and the draft stays for a retry — and keeps the file's CRLF
+  line endings and final newline. A file the editor cannot take (binary, or
+  over the 1 MB view cap) says so where the Edit button would be.
 - **Overview** — every changed file with its `+N −M`. Polls every 15s, because
   it is the cheap shape and the one you leave open while an agent works. Each
   row carries its own **stage** / **unstage** / **discard** buttons.
@@ -603,9 +614,14 @@ only one that answers "show me the code" rather than "show me the change"):
   a file that appears later is open by default; a lane switch clears it.
   Each file's header stays **pinned** at the top while its diff scrolls past,
   and carries the same stage / unstage / discard buttons as its overview row.
-  On a file with unstaged changes every `@@` row adds **Stage** and **Undo**
-  for that hunk alone (`stage-hunk` / `discard-hunk`); Undo asks twice, like
-  discard. The single-file view offers the same hunk buttons.
+  On a file with unstaged changes every hunk gets an editor-style **review
+  bar**, hung just under its last changed line and pinned to the visible
+  right edge: `^`/`v` to walk the hunks (each brings the next/previous `@@`
+  line to the top of the ONE scroller, below the sticky file header — a
+  review diff has no scroll box of its own unless it is large enough to
+  window, above 500 rows), `n of N`, **Undo**
+  (`discard-hunk` — asks twice, like discard) and **Keep** (`stage-hunk`).
+  The single-file view offers the same bar.
 - **One file** — clicking a file's path in any list opens just that file.
   **All files** returns to the list it was opened from — the same mode, at the
   same scroll offset — because reading a change-set is a walk down a long list
@@ -644,8 +660,8 @@ in every panel narrow enough to sit beside a console.
 **Per-file writes are the panel's, per-repo writes are the git bar's.** Staging
 one file means nothing unless a commit can take the index as it stands, so the
 overview grows a commit box the moment anything is staged — above the list and
-pinned while it scrolls, beside a **Stage all** that stages every listed file
-the index lacks in one call — it sends
+pinned while it scrolls, on ONE row with a **Stage all** that stages every listed file
+the index lacks in one call and an **Unstage all** that unstages every staged one — it sends
 `only: "staged"`, never `add -A`, and it is absent with a clean index because
 there is nothing it could mean. It is the dashboard's ONLY commit: the git bar
 above it has none, so no click can sweep the rest of the tree in with `add -A`. **Discard** is the one