docs: session headers name the harness and the model (displayModel)

- api-reference: the new `displayModel` session field, its sources in order
  (custom-endpoint, statusline, screen, launch) and that it is untrusted
  display text, persisted and restored when the CLI reported it.
- cli-registry: `capabilities.modelDetect` (one capture group, the last rows
  of the probe's capture, anchored on chrome only that CLI draws), the two
  stock patterns (dsh-TUI, codex) and the fifth config regex.
- architecture-invariants (tile grid): the header painter, the id as data, the
  untrusted model text, no writes for an unchanged session, the truncation
  order, Pane A's strip and its fits through syncTerminalGeometry.
- tile-grid-plan "as built", the wiki's Tile Grid page (logo and model rows,
  Split's strips), and CLAUDE.md's tile grid and CLI registry paragraphs.

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

docs/architecture-invariants.md

@@ -815,6 +815,8 @@ Further detail: with many sessions the horizontal strip stops being scannable, w
 
 ⚠️ **Chrome.** The header is a fixed 28px sibling of the body (its buttons are 26px targets with 16 to 19px glyphs, the app header's own icon-button size), refreshed in place on every tab render (`_renderSessionTabsImmediate` wrapper), never by rewriting the tile (that would take its xterm along) and never growing (#464: the body holds the xterm). Header buttons stop pointerdown, so acting on an unfocused tile does not focus it. × removes the tile only; killing stays behind the session menu's Close session. The `needs` pulse animates `box-shadow` only. Dividers are their own 6px grid tracks (`gap: 0`), tiles placed explicitly; a drag uses pointer capture, reflows the affected tiles locally per animation frame and sends ONE `fit()` (one PTY resize) per affected tile at pointer-up; closing the grid or removing a tile mid-drag tears it down. A tab dragged onto a tile replaces it (or swaps two tiles); tiles and empty slots handle `dragover`/`drop` in the CAPTURE phase and stop it, because the drag carries the session id as text and xterm's helper textarea would type it into the PTY.
 
+⚠️ **Harness and model.** Every session header (a tile's, both split panes') names the session's CLI with PR #532's `run-mode-dot <cliId>` logo slot and the model it runs as text, painted by ONE function, `_paintSessionHarness` (terminal-split.js), from the pure `describeSessionHarness` (constants.js). The id is data (the logo's class, the CLI catalog's label), never a branch: `test/frontend-cli-no-id-branching.test.ts` scans constants.js, terminal-split.js and tile-grid.js. The model is `SessionState.displayModel` (src/session-display-model.ts): the custom endpoint's `modelId`, else the newest report from the CLI itself (claude's statusline `model.display_name` via `POST /api/status-telemetry`, or the CLI's own footer read with `capabilities.modelDetect` off the capture the idle/working probe already takes), else the launch model, else nothing: the logo alone, never a placeholder. ⚠️ The model is untrusted, pane-derived text: sanitized and capped at 64 characters on the server, rendered with `textContent` inside a `data-i18n-skip` span; the tooltip (on the logo and on the model's box, which the translator may reach) says where a model the CLI did not report came from ("set at launch", "custom endpoint"), and the logo's accessible name carries harness and model so the model box is `aria-hidden`. ⚠️ The painter diffs against what it last wrote (kept on the header's parts), never the DOM, so an unchanged session writes nothing on a tab render. ⚠️ On a narrow header the model gives way first, then the name: the name does not shrink at all and is capped at its box (`max-width: 100%`), because any shrink factor takes a subpixel from a name that fits and ellipsizes it. ⚠️ Pane A's strip exists only while the split is open, as the first child of `.terminal-wrap`; it takes height from the main terminal, so opening and closing fit through `sendResize` / `syncTerminalGeometry` (#464), never a bare `fitAddon.fit()`, and the partial-history banner moves below it.
+
 ⚠️ **Attach.** A tile whose session has no PTY (`pid === null`) or whose socket closed because it exited (4009) shows an Attach overlay (absolute, the body keeps its size): `POST /interactive` (or `/shell`) with NO body, one in flight per session, a tripped PTY-exit breaker only through the same confirm as the single view, then the tile is remounted (a stopped socket cannot reconnect). The routes report a refusal in the ENVELOPE of a 200, so the response body is read, not `res.ok`. An agent that exited in a live pane (`paneExit`) cannot be started again in place (both routes refuse while the pane's tmux client runs): its tile shows the exit and points at Close session.
 
 ⚠️ **Persistence and joining.** `codeman:tile-grid` holds `{ v: 1, open, ids, focused, zoomed, colFr, rowFr }`, ids only, written as the grid changes; closing keeps it as `open: false` (the Tiles toggle, the picker and Ctrl/Cmd+click bring it back), the last tile leaving forgets it, a solo window never reads or writes it, an automatic zoom is not stored. Sessions created by THIS tab's Run join the open grid (`_joinTileGridFromRun`, called from session-ui.js `_ensureCreatedSessionVisible`; a wrapper from tile-grid.js would be overwritten by session-ui.js's later `Object.assign`); sessions created elsewhere arrive only by `session:created` and never join. ⚠️ A tile that joins that way connects BEFORE Run starts its pane: its resize reaches a session with no PTY, which `Session.resize()` only records (`_lastDesktopDims`) while the spawn uses a fixed 120x40, and Run's own resize step measures the parked main terminal (`display: none`, so `proposeDimensions()` is NaN and the step is skipped). Measured live: a 97x17 tile over a 120x40 pane. So `_renderTileChrome` remembers each tile's last-seen pid and calls `tile.paneStarted()` when it appears or changes (keyed on the sessions map, so a `handleInit` after an SSE drop counts too); `paneStarted()` forgets the sent size and sends it, and a hidden tile (a zoomed neighbour) sends nothing but keeps the size forgotten, so its next `fit()` sends it. A plain `fit({ force: true })` would lose that case. Tests: `test/tile-grid-*.test.ts` over the shared vm harness `test/mocks/tile-grid-vm.ts`.