feat(debug): ClaudePasteDetection dev module for #90 prompt-submit timing

[Juliusolsson05]

What

A ClaudePasteDetection dev-debug module on the existing #101 Dev Debug Panel framework, built to diagnose #90 (Claude prompt submit unreliable — detection falls behind under load). Pure instrumentation — no changes to the submit path itself.

Two panes:

1. Live detection — runs the actual submit-detection rules (/\[Pasted text #\d+/ placeholder + the spinner-activity regex) against the live runtime.screen / runtime.screenMarkdown each render, with the current streamPhase. Watch detection fire in real time.
2. Submit timeline — reads back the per-paste journals already written to <userData>/paste-debug/<pasteId>.paste.jsonl and reconstructs each submit's lifecycle: issued→detected latency, detected→CR, outcome (submitted/stuck/error), composer length, strategy — plus p50/p95 latency + failure count. This is Claude prompt submit still inconsistent — detection logic falls behind under load #90's "see the actual latency distribution" ask, surfaced from data we already capture but never read.

How

• readRecentPasteSessions() in pasteDebugJournal.ts + a dev-debug:read-paste-events IPC give the renderer-only module its main-process data (the journals were write-only at runtime).
• A pure timeline.ts reducer (PasteDebugSession → SubmitLifecycle + stats) holds all the digest logic — no React/IPC, keyed on the real event vocabulary (keydown:enter, placeholder:appeared|timeout, write:submit-cr, submit:returned|throw).
• The "stuck" signal is placeholder:timeout (the 10ms poller giving up) — exactly the failure mode Claude prompt submit still inconsistent — detection logic falls behind under load #90 chases.

Safety / scope

• Gated by AGENT_CODE_DEV_DEBUG; the 1s poll only runs while the module is mounted (enabled), so zero cost when off.
• Adds zero new typecheck errors (baseline 4 pre-existing remain).
• No new persistent test files (repo convention); verified via typecheck + manual acceptance.

Test plan

1. Run with AGENT_CODE_DEV_DEBUG=1; command palette → "Dev Debug Panel" → enable "Claude Paste / Submit Detection".
2. Paste + submit into a Claude pane → live regex panes toggle as [Pasted text #N] appears; timeline gains a row with issued→det latency + submitted.
3. Force a stuck submit under load → row shows stuck (red); failure count + p95 reflect it.

Refs #90, #101.

🤖 Generated with Claude Code