fix(tiles): a tile that joined before its pane existed resends its size

A session Run makes while the grid is open joins as a tile right away, so
the tile connects and sends its size before Run starts the pane. The
server only records a resize for a session with no PTY and spawns the pane
at 120x40, and Run's own resize step measures the parked main terminal
(display: none, so nothing). Measured live for Shell and Claude: a 97x17
tile over a 120x40 pane, for good (#464).

The chrome refresh now remembers each tile's last-seen pid and calls
TerminalTile.paneStarted() when it appears or changes. paneStarted()
forgets the sent size and sends it; a hidden tile (a zoomed neighbour)
sends nothing and keeps it forgotten, so its next fit() sends it, which a
plain fit({ force: true }) would lose. Keyed on the sessions map, so a
handleInit after an SSE drop counts too.

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

docs/architecture-invariants.md

@@ -811,7 +811,7 @@ Further detail: with many sessions the horizontal strip stops being scannable, w
 
 ⚠️ **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. Tests: `test/tile-grid-*.test.ts` over the shared vm harness `test/mocks/tile-grid-vm.ts`.
+⚠️ **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`.
 
 ### Gesture control: the setting
 

docs/tile-grid-plan.md

@@ -31,6 +31,10 @@ or settled a question the spec left open. The invariants as built are in
 - **4009 lands on the Attach overlay**, and 4003/4004/4010 remove the tile.
 - **"+ / New session in this case"** runs the normal Run for that case and joins through
   the same auto-join as any Run from this tab.
+- **A tile that joins before its pane exists resends its size when the pid appears**
+  (`TerminalTile.paneStarted()`): the server drops a resize for a session with no PTY and
+  spawns at 120x40, and Run's own resize measures the parked main terminal. Applying a
+  pre-spawn resize at spawn time on the server would make this unnecessary (follow-up).
 
 ## Problem