fix(run,terminal): merge-time fixes for the Instance count stepper and capture geometry

#454: the behaviour the PR adds had no test, so a regression test drives
runGrok() at tabCount 3 and asserts three quick-start POSTs with sequential
w<n>-<case> names (verified to fail against master's session-ui.js). Each
caller now reads the count BEFORE its opening banner and announces it there,
the way runClaude() already did, so a launch no longer prints two headers and
a launch with another session already active still says how many are starting.
runClaude() calls the shared _readTabCount() instead of its own copy of the
1..20 clamp, and that helper optional-chains the element read, since hoisting
it above each caller's try block would otherwise let a missing #tabCount throw
where the launch-error path cannot report it.

#435: sizeMovedUnderLoad derived from data.source alone. `mux-visible` is not
sufficient: a failed display-message cursor query makes capturePaneBuffer skip
the snapshot repaint and return the raw capture, which the route still labels
mux-visible, so a size that moved during such a load bought a full forced
reload to repair a frame that was never positioned. It now tests
Number.isFinite(data.captureRows) like its two siblings.

Plus the invariants and CLAUDE.md lines promised on #435: a visible capture
reports its geometry and omits it when nothing was positioned, the comparison
runs on mux-visible only, and the replay is capped at one attempt and latches
per session when it cannot converge.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.changeset/fix-report-the-captured-pane-geometry.md

@@ -4,44 +4,11 @@
 
 fix(terminal): replay a pane capture at the geometry it was taken at
 
-A visible-frame capture repaints each row at an absolute position, counting up
-to the pane's height and out to the pane's width. A terminal shorter than that
-clamps every address past its own height onto its last line, so the overflow
-rows overwrite one another and the rows underneath are lost. Against a 50-row
-pane, a 30-row terminal rendered 28 of a 45-line command and drew the surviving
-frame twice. A narrower terminal damages the same frame a second way: each row
-is painted out to the pane's own width, so the browser wraps every painted row,
-and the wrap on the last one scrolls the whole frame up by a row.
-
-Nothing in the response said what geometry the frame was built for, so the
-client could not detect either case. A capture now reports the geometry it was
-really taken at through `capturedGeometry` on `PaneCaptureOptions`, and the
-terminal response carries it as `captureCols` and `captureRows`. Both fields are
-absent unless the response really carries a capture, since a body that was never
-positioned has no geometry to describe. When a captured pane is taller or wider
-than the terminal, or the size that produced the capture did not survive the
-load, `selectSession` replays once at the size that stuck.
-
-That comparison runs on a visible-frame response only. A full-history response
-is linear scrollback closed by a relative cursor move, and a byte-history
-response carries no row alignment at all, so a size mismatch damages neither and
-a replay repairs neither. The distinction matters because the first load of
-every non-shell session per page takes the full-history path, where a replay
-would capture the whole tmux scrollback a second time.
-
-Two guards keep the replay to the one pass that can converge. `resizeRetry` caps
-it at a single attempt, so two competing fits cannot trade replays forever. A
-pane already drawing at the size the client just requested is left alone, which
-is the signature of a clamp rather than a race: `getTerminalDimensions()` floors
-at 40x10 while `fitAddon.fit()` does not, so a terminal narrower than 40 columns
-or shorter than 10 rows reports a pane permanently bigger than itself and would
-otherwise replay on every tab switch without ever converging.
-
-One case is still reported rather than repaired. A pane can be too tall because
-`Session.resize` declined the resize outright, which it does for a small
-viewport while a desktop viewport's size claim is live. The retry re-sends the
-same declined resize and captures the same pane, so it costs the one capped
-attempt and the frame is shown as it is. Repairing it means deciding who owns
-the pane size while a desktop claim is live, which is a policy question this
-does not touch. The reported geometry still helps, because the client can see
-the mismatch at all rather than being blind to it.
+Opening a session could draw a frame built for a pane bigger than your terminal. A
+taller pane wrote its overflow rows onto the last line and lost the rows underneath
+(against a 50-row pane, a 30-row terminal rendered 28 of a 45-line command and drew
+the survivors twice), and a wider one wrapped every row and scrolled the whole frame
+up by one. The terminal response now reports the geometry the capture was really
+taken at, so the browser can see the mismatch and replay once at the size that stuck.
+A pane that cannot be sized to fit is diagnosed once per session instead of on every
+tab switch.

.changeset/run-instance-count-non-claude.md

@@ -0,0 +1,11 @@
+---
+"aicodeman": patch
+---
+
+fix(run): make the Instance count stepper work for every non-Claude mode
+
+The Instance count stepper next to the Run button only ever applied to Claude.
+Setting it to 3 and launching OpenCode, Codex, Gemini, Antigravity, Pi, OMP, Grok or
+DeepSeek started exactly one session, with no error and no hint that the control had
+done nothing. All eight now launch the count you asked for, and the opening banner
+says how many are starting.