[jefft72]

Summary

Introduces native plans as a first-class coding-agent artifact with a bounded schema, normalized content, an intrinsic submit_plan tool, and an explicit implementation authorization prompt.
Extends append-only session history so collaboration mode, submitted plan drafts, user resolutions, and accepted implementation continuations survive JSONL reloads and branch replay.

Reasoning

Plan state must remain durable and branch-local because a user can resume, fork, compact, or navigate a session before deciding whether to implement a submitted plan.
Reconstructing that state from validated lifecycle entries prevents a plan from being lost, resolved against the wrong branch, or treated as implementation authority before the user explicitly accepts it.

Persisted artifacts also form a trust boundary.
Strict size, control-text, parentage, and transition checks keep malformed or tampered session data from silently changing collaboration policy or creating an ambiguous continuation.

Changes

• Adds CollaborationMode, PlanArtifact, and PlanResolution contracts with limits for plan IDs, titles, and Markdown bodies.
• Normalizes plan titles to a trimmed single line, preserves trimmed Markdown structure, rejects unsafe control and bidirectional text, and freezes parsed artifacts before use.
• Adds the sequential intrinsic submit_plan tool with a typed input schema and a result that returns the exact persisted artifact.
• Adds createPlanImplementationPrompt so accepted plans become an explicit, decision-ready implementation instruction instead of an implicit state change.
• Extends session history with collaboration-mode, plan, and plan-resolution entries and exposes pending plan and continuation state through SessionContext.
• Replays plan lifecycle state along each entry's parent chain, returns to default mode on resolution, and retains an implementation continuation only until its next user message consumes it.
• Rejects invalid lifecycle transitions, mismatched resolutions, duplicate entry IDs, missing parents in plan-aware sessions, and invalid persisted plan artifacts before indexing the session.
• Adds append APIs for each lifecycle entry and rolls back the in-memory entry list, index, and leaf when persistence fails.
• Excludes plan lifecycle metadata from branch-summary conversation content while preserving the state needed for deterministic replay.
• Covers tool normalization, unsafe text rejection, implementation prompts, JSONL round trips, malformed primitive lines, and duplicate-ID protection.

Testing

• Final rebased stack: npm run check passed.
• Final rebased stack: focused Vitest validation across 28 affected files passed all 451 tests.
• This intermediate branch was not checked independently after reconstruction.

[jefft72]

Closing to rebuild on a clean base.

This stack does not build. Two separate defects are present, and the first masks the second:

1. A stray closing brace committed in feat: enforce native plan collaboration policy #64 stops packages/coding-agent/src/core/agent-session.ts from parsing at all.
2. From feat: activate accepted plans in routed sessions #65 onward the stack imports five modules that exist only on the task profile stack: evolved.ts, harness-descriptors.ts, profile-router.ts, profiles.ts, and runtime-telemetry.ts.

Replacement stacks:

• plan/* for native plan mode standing alone on main
• plan-harness/* for the plan and profile integration

The branch behind this PR is retained unchanged as a backup.