docs: add SDD verify report for responsive terminal

openspec/changes/responsive-terminal/verify.md

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+# Verify: Responsive Web Terminal
+
+## Verification Report
+
+### What Changed
+
+Implemented a resilient, responsive web terminal with auto-reconnect, heartbeat, local echo, and scrollback persistence across 3 chained PRs.
+
+**Backend (PR-1):**
+- `terminal_session.py`: Added termios echo detection, exit reason tracking, `closed` public property
+- `terminal_manager.py`: Added heartbeat tracking (15s ping / 60s idle timeout), message batching (16ms), ping/pong handling, task reference storage
+- `terminal.py`: Added ping/pong routing, echo state checks, `session_ended` notification
+
+**Frontend (PR-2):**
+- `use-terminal-connection.ts`: WebSocket lifecycle, exponential backoff reconnect, heartbeat, local echo deduplication, resize debounce/throttle, scrollback callbacks, `Ctrl+Shift+R` shortcut
+- `use-terminal-connection.test.ts`: 13 tests covering connection lifecycle, reconnect backoff, resize, scrollback
+
+**Frontend UI (PR-3):**
+- `terminal.tsx`: Rewritten with status bar, session-ended overlay, reconnect banner, ResizeObserver, light/dark theme, xterm-addon-serialize
+- `styles.css`: Added overlay, reconnect banner, spinner animation styles
+
+**Documentation:**
+- `docs/features/terminal.md`: User guide with connection states, keyboard shortcuts, troubleshooting
+- `docs/architecture/frontend.md`: Terminal component stack and data flow
+- `docs/architecture/backend.md`: Terminal system architecture and protocol
+
+### Acceptance Criteria Coverage
+
+| AC | Status | Evidence |
+|----|--------|----------|
+| AC-1: Auto-reconnection | ✅ | Implemented in `useTerminalConnection` — 1s→30s backoff, max 10 attempts |
+| AC-2: Heartbeat | ✅ | 15s ping interval, 5s pong timeout, 60s idle close on server |
+| AC-3: Local echo | ✅ | Printable ASCII echoed immediately, server deduplication, echo-state control |
+| AC-4: Resize debounce | ✅ | 200ms debounce + 500ms throttle in `sendResize` |
+| AC-5: Scrollback serialization | ✅ | `SerializeAddon` + `sessionStorage` + restore with divider |
+| AC-6: Connection quality indicator | ✅ | Status bar with color-coded dot, latency tooltip, attempt counter |
+| AC-7: Graceful container exit | ✅ | `session_ended` message + overlay with Reconnect/Go Back |
+| AC-8: Backend message batching | ✅ | 16ms batch window in `_read_loop` |
+| AC-9: Keyboard shortcut | ✅ | `Ctrl+Shift+R` triggers `reconnect()` |
+
+### Quality Gates
+
+| Gate | Result |
+|------|--------|
+| Frontend typecheck | ✅ Clean |
+| Frontend lint | ✅ Clean |
+| Frontend tests | ✅ 48 passed (13 new hook tests) |
+| Backend unit tests | ✅ 101 passed (16 new terminal tests) |
+| Backend ruff | ✅ Clean |
+
+### Commits
+
+- `6c8cfe9` — `feat: responsive web terminal with auto-reconnect, heartbeat, and local echo`
+- `a01e625` — `docs: add responsive terminal documentation`
+
+### Risks and Limitations
+
+- Docker exec PTY is not resumable across reconnects — new shell is spawned. Scrollback serialization makes this transparent.
+- Local echo only works for printable ASCII; control chars and escape sequences round-trip.
+- `termios` echo detection is Unix-only (Linux/macOS). The fallback is echo-enabled.
+- Integration tests require Docker + running containers; not covered in automated test suite.
+
+### Follow-ups
+
+- [ ] Manual end-to-end testing with real containers
+- [ ] Consider adding `xterm-addon-webgl` for GPU rendering on high-latency connections
+- [ ] Consider scrollback persistence across full page reloads (currently `sessionStorage` only)