Reusable ACP session stream

Traceability

• Spec ID: acp-session-stream
• Status: Implemented
• Request: improve the Compare ACP flow using the supplied ACP/AHP gap analysis and local VS Code source.

Intent

Compare and Debugger should share one session stream with readable messages, inspectable tools, explicit pending decisions, and observed ACP session state. The supplied plan is a gap analysis, not an accepted implementation plan for an entire session manager. This change closes its incoming-update and stream UX gaps within the current single-run Studio contract.

Reference inspected: local VS Code chatListRenderer.ts separates thinking, tool invocations and confirmation states; chatWidget.ts retains whether the reader is at the bottom. Adopt those interaction boundaries without importing VS Code code or AHP channels. The installed ACP v1 SDK schema owns update shapes; its plan_update and plan_removed variants are explicitly unstable.

Acceptance Scenarios

• AC-1: Compare and live ACP Debugger render the same reusable stream component. It receives state and action callbacks; it does not own agent selection, project routing, or launch requests.
• AC-2: Responses and collapsible thoughts retain arrival order; tools disclose input/result and terminal status, including late tool updates. The submitted prompt remains visible after the composer changes.
• AC-3: Valid incoming plan snapshots, usage/context and reported cost, commands, current mode, config values and session metadata are projected incrementally. Empty snapshots clear state; absent metadata is never invented. Malformed, truncated and unsupported updates do not crash or masquerade as full support.
• AC-4: Each lane owns its permission queue and pending action. Decisions are never auto-approved, duplicates are disabled while sending, HTTP failures remain visible and retryable, and terminal runs clear obsolete decisions.
• AC-5: Appended content and progressive text follow only while at the bottom. Scrolling back preserves position; a keyboard-accessible latest button resumes following. Completed/error streams settle busy message/tool state.
• AC-6: Concurrent lanes fold independently, duplicate launch is prevented, and failed or prematurely closed streams keep partial evidence and show failure.
• AC-7: Wide, compact and narrow layouts have bounded overflow, visible focus, actionable permission controls, and no console/page errors. Shared styles use existing semantic tokens and both English and Chinese labels.

Non-goals and remaining gaps

Cross-restart session catalog/load/resume/delete, multi-turn/fork, auth, outgoing rich attachments, MCP hosting, mode/config mutation, PTY, AHP, and ACP v2 remain separate host/API work. Commands/config are observed state, not enabled actions. Protocol evidence is bounded/redacted; this projection does not promise complete session persistence, and agent-reported cost is not billing verification.

Plan and Tasks

1. Add validated ACP observation projection under Studio app/run and fold it at the existing sequenced protocol-event boundary (both Node and Rust). Emit thought text through the normal message framing with optional role: "thought" from both executors; role transitions close the previous message. Keep it out of the executor's final answer and retain its identity in saved Debugger records. This avoids merging independently scheduled wire evidence and transcript callbacks into one apparent conversation order. Accept the native serde enum's snake_case tool fields in the Rust bridge, retaining compatibility with camelCase client fixtures.
2. Extract reusable timeline entries and a session stream; compose it from Compare and Debugger while retaining their independent host controls.
3. Correct permission/action failure and stream completion handling. Mark native raw permission frames permissionActionable: false in the neutral protocol envelope; preserve their RPC evidence while only exposing the host-owned request as an actionable decision. The parser retains this optional annotation across SSE.
4. Add reducer/transport and real fixture browser tests; build and inspect screenshots. Review only this task's diff against the pre-existing dirty tree.

Test and Review Evidence

• AC-1–AC-7: npm run build --workspace=@qoder-ai/harness-studio and Studio npm run typecheck passed. Earlier transient build failures in a concurrently edited Git view are superseded by this successful full build.
• AC-2–AC-4, AC-6: 28 tests passed across the Studio session projection, run-action, run-store, stream transport, tool payload, streaming-text and retained-record transform tests. Another 25 Harness event/protocol/SDK tests passed, including the existing serialization/lifecycle contracts. Projection tests exercise Node and Rust response shapes, empty snapshots, malformed values, independent permission queues, wire-only permissions, late tool input/result, and thought settlement.
• AC-1, AC-4–AC-7: 10 Playwright tests passed in acp-debugger.spec.mjs and acp-session-stream.spec.mjs. The runtime attachments confirmed Node stdio, the staged native Rust host, and the staged macOS NSXPC service. These are fixture-agent receipts, not installed commercial-agent qualification.
• AC-2–AC-4: both rich-stream browser tests also passed with the staged Rust stdio host explicitly selected through STUDIO_TEST_ACP_HOST. The native executor regression passed both tests and covers serde tool fields, message/thought/tool order, final output excluding thoughts, and non-actionable raw permission evidence through both stdio and NSXPC.
• AC-2, AC-7: the existing keyboard-expandable failed/truncated Tool Call browser regression also passed after extracting the shared entry renderer.
• AC-5: rich stream tests passed twice consecutively after exercising progressive text growth, upward reading, continued streaming without position theft and keyboard return to latest. A later error-placement adjustment passed the full 10-test browser set above.
• AC-7: reviewed Compare and Debugger screenshots at 1440×900, 1024×768 and 390×844, including light/dark themes. Assertions cover console/page errors, keyboard focus, document/transcript overflow and non-overlapping stacked lanes. The expected 503 responses in failure/retry tests are explicitly excluded from console-error counting. Reduced-motion preference disables progressive reveal.
• Additional ego-browser inspection of the shared Debugger stream at 200% CSS zoom retained a 1200px document in a 1200px viewport and a readable completed fixture response. This is CSS zoom evidence, not a native browser zoom test.
• Preview: npm run preview found the existing server on 58575; /health and /canvas-module.js both returned 200. No existing preview process was stopped.
• Documentation: routing graph regenerated with no diff; all 8 doc-link tests passed. git diff --check passed.

Review readiness

This is a user-requested maintenance feature without a supplied Story id. The spec and observed tests cover the scoped diff. AI assistance is explicit in this Codex task and the commit co-author. The user authorized committing this change after implementation validation; no push, installation or release is included. Concurrent work touched the composer, shell, Git view and customization view; those changes were preserved and are outside this review.

Screenshots are retained under the task's acp-session-stream visualization directory. Tests accept STUDIO_TEST_APP_DIR so an isolated application build can be used while other local tasks rebuild the shared distribution.

Risk: raw protocol evidence can be incomplete. Projection accepts known shapes, preserves the redaction boundary and reports incompleteness. Native OS host qualification remains distinct from local browser/fixture evidence.