Easy Message Unqueue with /unqueue - #6415

New SessionV2.pending/withdraw/revise methods let a caller remove or
edit a message that's been durably admitted but not yet promoted into
a visible turn -- plus three new HTTP routes and a TUI /queue dialog.

Ported from upstream anomalyco#4821 (126 reactions): PR anomalyco#6415
"Easy Message Unqueue with /unqueue" (closed by a 60-day-stale bot,
never reviewed) and PR anomalyco#6271 "add edit and discard actions for queued
messages" (more thorough, self-closed after apparent lack of
maintainer response). Both PRs remove a queued message from an
in-memory callback list and delete the V1 message -- a backend model
with no equivalent in this repo's V2 session core, where a queued
message is a durable row that stays pending until a safe promotion
point. So the backend here is a fresh, V2-native design, not a port:
a durable event (session.next.prompt.withdrawn / .revised) is
published and projected the same way SessionInput.Prompted already
works, guarded to only affect rows that are neither promoted nor
withdrawn, with a withdraw winning any race against an in-flight
promotion. What was reused: the remove/edit concepts themselves,
/unqueue kept as a command alias (anomalyco#6415), and the general shape of a
queued-message picker UI (anomalyco#6271) -- reworked as a /queue list dialog
rather than anomalyco#6271's inline "EDITING" mode in the main prompt box.

New requireInput flag threads through the turn loop in
packages/core/src/session/runner/llm.ts so a turn whose only
justification was a withdrawn input is skipped rather than run with
nothing to answer -- merged by hand against this fork's own
model-fallback feature, which had already added a different
parameter (tried) to the exact same functions.

KNOWN, SIGNIFICANT GAP: the TUI still sends every prompt through the
legacy V1 SessionPrompt path, which never creates the V2 session_input
rows this feature acts on. /queue will show an empty list for
anything typed in the actual running TUI today. Switching the TUI to
send V2 prompts is a materially bigger decision than this feature's
own scope and was deliberately left for a separate follow-up rather
than silently expanded into. The backend is fully real, tested, and
reachable via the HTTP API directly today.

New tests: packages/core/test/session-prompt.test.ts (+10 cases),
session-runner.test.ts (+4), packages/tui/test/cli/tui/data.test.tsx
(+2), three new httpapi-exercise scenarios, event-manifest count
updated (88 -> 90 for the two new durable events). Client and legacy
JS SDKs regenerated. Verified against this fork's current dev,
including the manual merge against model-fallback: bun typecheck
clean across all 30 packages; packages/core 1178 pass (only the
pre-existing pty flake); packages/opencode 3613 pass, only the 4
pre-existing cf-ai-gateway failures; packages/tui 230 pass;
httpapi-exercise coverage mode 214 pass.

Co-Authored-By: Claude Sonnet 5 <[email protected]>