test(terminal): follow the existing suites to the one geometry owner

The gate caught fourteen failures the focused tests could not: every harness
that builds a partial app out of cherry-picked mixin methods, and every source
guard that named `fitAddon.fit()` by hand.

Most are wiring — `syncTerminalGeometry`, `_refitAfterCellSizeChange` and
`_resizeTerminalTo` added to the fakes so the real chain runs rather than a
stub of it. `file-browser-search` is the one that shows why it matters: without
the method on the fake, selectSession's unconditional call threw into its own
catch and every later assertion in the file measured a load that never
happened.

Two are not wiring.

`detached-session-pane-sizing` pinned the behaviour this change deliberately
reverses. It asserted the LOCAL fit still runs for a session owned by its own
window — "withhold the send, never the reflow" — so the assertion is restated
rather than patched, with the reason beside it and in the file's docblock: a
reflow the PTY is never told about leaves this xterm rendering a CLI's frames
against a shape that does not exist, and the popup that owns the pane is
drawing for its own width regardless. The old rule bought a garbled frame, not
a correct one.

`mobile-prompt-composer` sliced `_cleanupSessionData` as a fixed 1200-character
window, so the assertion depended on how much unrelated code sat above the line
it cared about. It reads the whole method now.

`terminal-scroll-intent` records `syncTerminalGeometry` rather than `fit`,
under its own name: recording a bare fit there would name the very thing the
subject was changed to stop doing.

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

test/mobile-prompt-composer.test.ts

@@ -223,7 +223,12 @@ describe('mobile prompt composer', () => {
 
   it('wires session cleanup to composer draft cleanup', () => {
     const cleanupStart = appSource.indexOf('  _cleanupSessionData(sessionId) {');
-    const cleanup = appSource.slice(cleanupStart, cleanupStart + 1200);
+    expect(cleanupStart, '_cleanupSessionData not found — renamed?').toBeGreaterThan(-1);
+    // The whole method, not a fixed byte window. A 1200-character slice made
+    // this assertion depend on how much OTHER code sat above the line it cares
+    // about, so an unrelated addition near the top of the method failed it.
+    const cleanup = appSource.slice(cleanupStart, appSource.indexOf('\n  }\n', cleanupStart));
+    expect(cleanup.length, 'method body did not terminate').toBeGreaterThan(0);
 
     expect(cleanup).toContain('KeyboardAccessoryBar.discardComposerDraft?.(sessionId)');
   });