Remove deferred condensation and add trailing transcript handling

[khaong]

Summary

• Remove ACTIVE_COMMITTED phase from session state machine — checkpoints now condense immediately on GitCommit regardless of session phase (no more deferred condensation)
• Remove PendingCheckpointID from session state — simplifies PostCommit to single-pass, PrepareCommitMsg to fresh-ID-only, and HandleTurnEnd to no longer dispatch ActionCondense
• Add trailing transcript handling — post-commit conversation (summaries, explanations) with no new file edits is appended to the prior checkpoint via new UpdateCommitted operation
• Update documentation — CLAUDE.md, architecture docs, and regenerated state diagram reflect the simplified lifecycle

30 files changed, 1325 insertions, 1106 deletions across 6 commits.

Design

See docs/plans/2026-02-13-checkpoint-boundary-realignment-design.md for full design rationale.

Before: ACTIVE + GitCommit → ACTIVE_COMMITTED (deferred condensation at TurnEnd)
After: ACTIVE + GitCommit → ACTIVE + [Condense, MigrateShadowBranch] (immediate condensation)

Test plan

• Unit tests for state machine transitions (ACTIVE_COMMITTED removed, backward compat via PhaseFromString)
• Unit tests for trailing transcript guards (no LastCheckpointID, new files touched, no new transcript, successful append)
• Unit tests for UpdateCommitted (append transcript, not-found, multi-session matching)
• Integration tests for trailing transcript (appended when no new files, skipped when new files touched)
• Integration tests for immediate condensation flow (commit-before-stop)
• mise run fmt && mise run lint && mise run test:ci all pass

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR simplifies the session state machine by removing the ACTIVE_COMMITTED phase and implementing immediate condensation during commits instead of deferred condensation. It also adds trailing transcript handling to capture post-commit conversation that belongs to the condensed checkpoint.

Changes:

• Removes ACTIVE_COMMITTED phase from the state machine, with backward compatibility for old state files
• Removes PendingCheckpointID field from session state, simplifying checkpoint ID management
• Implements immediate condensation on GitCommit events (ACTIVE + GitCommit stays ACTIVE, condenses immediately)
• Adds trailing transcript handling via new UpdateCommitted operation to append post-commit conversation to checkpoints
• Updates all related tests, integration tests, and documentation to reflect the simplified lifecycle

Reviewed changes

Copilot reviewed 29 out of 30 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
cmd/entire/cli/session/phase.go	Removes ACTIVE_COMMITTED phase constant, adds backward compatibility mapping to ACTIVE
cmd/entire/cli/session/state.go	Removes PendingCheckpointID field from State struct
cmd/entire/cli/checkpoint/committed.go	Adds UpdateCommitted method and helper functions to append transcript/prompts to existing checkpoints
cmd/entire/cli/strategy/manual_commit_hooks.go	Refactors PostCommit to condense immediately on ACTIVE+GitCommit; updates HandleTurnEnd to handle trailing transcripts
cmd/entire/cli/strategy/manual_commit_trailing.go	New file implementing handleTrailingTranscript logic with guards and idempotency
cmd/entire/cli/integration_test/trailing_transcript_test.go	New integration tests verifying trailing transcript append and skip scenarios
cmd/entire/cli/strategy/phase_postcommit_test.go	Updates unit tests for immediate condensation behavior, removes deferred condensation tests
cmd/entire/cli/strategy/phase_prepare_commit_msg_test.go	Updates tests to use LastCheckpointID instead of PendingCheckpointID
CLAUDE.md	Updates architecture documentation to reflect simplified state machine
docs/architecture/claude-hooks-integration.md	Documents trailing transcript handling in TurnEnd hook

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Deprecated exported variable is unused throughout codebase

Low Severity

The exported PhaseActiveCommitted variable is declared as deprecated but has zero references anywhere in the codebase — all usages were migrated to raw Phase("active_committed") strings or removed. The comment claims it's kept "so that external packages referencing it continue to compile during the migration," but since no package references it, it's dead code that could confuse future readers into thinking the phase is still meaningful.