feat(quick-pane): add constrained agent window

docs/quick-pane-v1-design.md

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+# Quick Pane v1 Design
+
+## Goal
+
+Quick Pane is a small native window opened by a desktop/window-manager hotkey. It accepts one short request and returns either a useful answer or an explicit escalation within 60 seconds.
+
+## Scope
+
+- Cold-launchable, independent Tauri window.
+- Compact request input, quick-model picker, and workspace picker.
+- Configured default workspace, quick model, follow-up model, supplemental prompt, time limit, and read-only tool limit.
+- Ephemeral Quick Pane UI state and best-effort runtime cleanup.
+- Advisory read-only/no-subagent instructions, inline permission/clarification prompts, and explicit normal-session handoff.
+
+## Non-goals
+
+- Persisted quick history.
+- Named profiles.
+- App-managed WM binding writes.
+- Trusted prevention of mutable tools or direct edits.
+- Trusted prevention of subagents.
+- A memory-only Pi runtime; Pi may write temporary session data while running.
+
+## Invocation
+
+Desktop/WM configuration owns the hotkey so it works while Pi GUI is absent. Settings displays and copies the required command; it does not register or modify system bindings.
+
+The app creates or focuses a dedicated small Quick Pane window. `Esc` closes it and discards quick-only state.
+
+## Request lifecycle
+
+1. Pane chooses configured default workspace and quick model, with per-request overrides.
+2. It starts an isolated Pi RPC runtime in the chosen workspace.
+3. Immutable prompt text instructs one request, read-only inspection, zero subagents, configured wall-clock budget, and configured tool-call budget. Current Pi RPC cannot trusted-enforce those instructions; event-derived caps and cleanup are best effort.
+4. Supplemental user instructions append beneath those prompt guardrails.
+5. Pane streams answer, tool status, and inline extension requests.
+6. On success it displays final answer. On a cap it preserves partial answer, explains the cap, and offers handoff.
+
+## Escalation
+
+Mutations, subagents, multi-step work, and likely-over-budget work preflight-escalate. The quick agent explains why. The user clicks **Continue in full session** to open a new normal session with:
+
+- original request;
+- escalation note or partial findings;
+- selected workspace; and
+- configured follow-up model.
+
+No full session opens automatically.
+
+## Permissions and privacy
+
+Quick Pane surfaces Pi extension `select`, `confirm`, `input`, and `editor` requests inline. User explicitly answers every prompt. Existing policy remains authoritative: ordinary workspace reads may be allowed, external-directory reads may ask, and sensitive paths may deny.
+
+Quick Pane UI request, output, and transcript stay in memory only. Closing pane removes them and triggers best-effort quick-runtime cleanup. Pi may write temporary session data while the child runs. A deliberate handoff persists only in newly created normal-session history.
+
+## Failure handling
+
+Unavailable models, startup failures, and crashes render inline actionable errors: retry, pick another quick model, or open normal session. No silent fallback model is used.
+
+## Settings validation
+
+Settings reject invalid model, workspace, custom prompt, or numeric limit. Failed save keeps previously stored configuration and marks invalid fields.
+
+## Acceptance
+
+From cold or hot desktop state, the hotkey produces an answer or explicit escalation within 60 seconds. Automated component, bridge, persistence, and native tests cover behavior; a manual cold-launch/hotkey smoke test verifies desktop integration.

docs/quick-pane-v1-implementation-plan.md

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+# Quick Pane v1 Implementation Plan
+
+## 1. Define persisted configuration
+
+- Add Quick Pane settings types, defaults, validation, serialization, and migration-safe native storage.
+- Fields: default workspace, quick model, follow-up model, supplemental prompt, maximum seconds, maximum read-only tool calls.
+- Preserve current configuration when validation or save fails.
+
+## 2. Add native window and launch contract
+
+- Extend Tauri configuration and Rust window management with a dedicated Quick Pane window label.
+- Add command-line action used by external WM hotkey to create/show/focus pane, including cold launch.
+- Keep `--toggle` and ordinary `--new` behavior unchanged.
+
+## 3. Build Quick Pane React surface
+
+- Add isolated state reducer/component for request, selected model/workspace, progress, final answer, partial answer, escalation, extension UI, and errors.
+- Keep pane transcript in component memory only and request best-effort runtime/session cleanup on close.
+- Add Settings controls and copyable WM launch command.
+
+## 4. Add constrained bridge runtime mode
+
+- Extend runtime creation with Quick Pane metadata and ephemeral session lifecycle.
+- Build immutable advisory quick-agent instructions around supplemental custom prompt.
+- Use observed tool events and wall-clock cancellation for best-effort caps; document that current Pi RPC cannot trusted-enforce read-only/no-subagent policy or memory-only runtime sessions.
+- Instruct preflight escalation for mutation, subagent, multi-step, or likely-over-budget requests.
+
+## 5. Route interaction and handoff
+
+- Reuse existing extension request/response protocol for inline Quick Pane permission and clarification dialogs.
+- On explicit continuation, create normal runtime using workspace and follow-up model.
+- Prefill it with original request plus escalation note/partial findings.
+
+## 6. Test and document
+
+- Add unit tests for settings validation/persistence and guardrail classification.
+- Add component tests for pane states, picker behavior, inline prompts, error/retry, and cleanup.
+- Add Rust/bridge tests for window command routing, budget cancellation, ephemeral cleanup, and handoff payload.
+- Add manual WM hotkey/cold-launch instructions and smoke checklist.
+
+## Sequencing
+
+Land configuration/runtime contract first, then native window and UI, then handoff and test coverage. Preserve existing normal-session paths throughout.

docs/quick-pane-v1-test-plan.md

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+# Quick Pane v1 Test Plan and QA Checklist
+
+## Automated coverage
+
+### Settings
+
+- Valid defaults load when no Quick Pane configuration exists.
+- Valid configuration round-trips through native storage.
+- Invalid workspace, model, prompt, time, and tool values show field errors and retain prior saved state.
+- Quick model picker affects quick request only; follow-up model remains configured default.
+
+### Runtime guardrails
+
+- Quick runtime receives immutable advisory read-only/no-subagent prompt text plus supplemental prompt.
+- Mutation, subagent, multi-step, and likely-over-budget requests are instructed to preflight-escalate.
+- Runtime applies best-effort configured 60-second/6-tool caps from observed events and exposes reason.
+- Partial result survives a cap; pane transcript is removed and runtime cleanup requested after pane close.
+- Tests/documentation state current limitations: Pi RPC cannot trusted-enforce prompt policy or guarantee memory-only temporary sessions.
+
+### UI and bridge
+
+- Quick Pane opens/focuses through dedicated native command without changing normal `--new` or `--toggle` behavior.
+- Workspace and quick-model picker values reach runtime creation.
+- Permission and clarification extension requests render inline and send correct response payloads.
+- Retry, model change, and normal-session actions appear for startup/model/crash errors.
+- Handoff creates normal session with original request, escalation note, workspace, and follow-up model.
+
+## Manual smoke checklist
+
+1. Configure default workspace, models, prompt, and 60-second/6-tool limits.
+2. Add desktop/WM hotkey using Settings launch command.
+3. From no running GUI process, invoke hotkey and verify Quick Pane opens/focuses.
+4. Submit short answer-only request; verify result within 60 seconds.
+5. Submit read-only inspection request; answer any external-read permission prompt inline.
+6. Submit mutation or multi-step request; verify reason and **Continue in full session**.
+7. Continue; verify normal session receives handoff and follow-up model.
+8. Close Quick Pane; reopen and verify quick transcript is absent.
+9. Select unavailable model or induce startup failure; verify inline recovery options.
+
+## Exit criteria
+
+All targeted automated tests pass. Manual cold-launch/hotkey smoke completes. No regressions in normal sessions, `--toggle`, or `--new` behavior.