fix(release): the seven findings from the pre-release review of the whole tree

A full review of the release tree found seven things, and four of them were mine.

**The gate was red, and I put it there.** Splitting `confirmed` into `confirmedContext`
and `confirmedSwap` changed the wire field without moving three assertions that check
it: `custom-model-one-shot-launch.test.ts` and two in `custom-model-run-menu-ui.test.ts`
(the swap modal and the context modal, each of which already receives exactly the right
per-question flag). Moved, with the titles.

**Worse, my own tests for the split never ran.** The four cases in
`session-custom-model.test.ts` that exist specifically to pin it call `mockRunning()`,
which was declared inside a sibling `describe`, so they threw a ReferenceError during
setup. The split would have shipped with no passing server-side coverage while the gate
reported the failure as four broken tests rather than as four tests that were never
written. `mockRunning` is hoisted to the outer describe.

**The submit verifier pressed Enter into shell panes.** `#455`'s SubmitVerifier resolved
its composer glyph as `promptGlyph ?? '❯'`, and only claude and codex declare one, so
the other eight modes fell back to claude's `❯`. That is also starship's default shell
prompt, and pure's, and spaceship's, and p10k lean's. On such a shell the line
`❯ npm run build` sits on screen for as long as the command runs, the verifier reads it
as an unsubmitted prompt, and re-presses Enter into the running program's stdin up to
nine times on its 2s..60s schedule. Mostly a stray newline; not harmless against a y/N
prompt, `read -p`, an installer or a pager, where it takes the default. The module's own
fileoverview already stated the rule this broke. Now `?? ''`, which
`promptStillInComposer()` already treats as inert, so the verifier runs only for a CLI
that actually declares a composer.

**My #451 dedent removal left a count behind**: "Two rules keep it honest" introducing
three numbered rules.

The rest is documentation the split outran. `confirmedContext`/`confirmedSwap` appeared
in no doc at all, while `docs/api-reference.md` (the SemVer-covered contract) still told
an integrator to retry with `confirmed: true` for both questions, which is precisely the
thing the split exists to stop. Documented there, in `docs/custom-model-endpoints.md`
and in CLAUDE.md. The custom-model changeset gained the split and the `CLAUDE_CONFIG_DIR`
multi-user consequence, both user-visible and both previously absent, and #454's gained
the one exception to its own claim: a Custom Endpoints launch ignores the Instance count
stepper and always starts one session.

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

src/session.ts

@@ -3758,7 +3758,18 @@ export class Session extends EventEmitter {
           ? null
           : this._mux.capturePaneText?.(this._muxSession.muxName),
       sendEnter: () => this._mux?.sendInput(this.id, '\r'),
-      glyph: () => getCli(this.mode)?.capabilities.workDetect?.promptGlyph ?? '❯',
+      // ⚠ NO fallback glyph here, unlike the screen-reading probe elsewhere in this file.
+      // Only claude and codex declare a promptGlyph; the other eight modes would fall back
+      // to claude's `❯`, which is ALSO starship's default shell prompt (and pure's, and
+      // spaceship's, and p10k lean's). On a shell session the line `❯ npm run build` sits
+      // on screen for as long as the command runs, promptStillInComposer() reads that as
+      // "still unsubmitted", and the verifier presses Enter into the running program's
+      // stdin on its 2s..60s schedule. Mostly a stray blank line; not harmless against a
+      // y/N prompt, `read -p`, an installer or a pager, where it takes the default.
+      // promptStillInComposer() returns undefined for an empty glyph, so this makes the
+      // verifier inert for every CLI that does not declare one, which is what the Claude
+      // Code 2.1.277 defect it exists for actually calls for.
+      glyph: () => getCli(this.mode)?.capabilities.workDetect?.promptGlyph ?? '',
       log: (m) => console.log(`[Session ${this.id.slice(0, 8)}] ${m}`),
     });
     this._submitVerifier.arm(text);