Phase 1 of approved feature #1817. Implements the body-structure
derivability contract landed in ADR-1817 (Phase 0, PR #1828).
Source changes (src/state-transition.cts):
- Add `rebuild` as the 11th intent in StateTransitionIntent (ADR-1769
transition set extended per ADR-1817 §1).
- Add `phaseInventoryProvider` optional dep + PhaseInventoryRecord type
(Leaky-Abstractions guard: pure core stays testable without disk I/O;
rebuild skips table reconciliation when the provider is absent).
- Add `case 'rebuild':` dispatch arm to transitionCore (the missing-case
compile-time guarantee extends to the 11th case).
- Implement rebuildCore orchestrator + four drift-class helpers per
ADR-1817 §2:
* reconcileCurrentPosition — body prose re-derived from frontmatter
* reconcileByPhaseTable — **By Phase:** table re-derived from disk
inventory via the new dep
* stripTemplatePlaceholders — `**Field:** [placeholder]` →
`**Field:** (pending)` (no canonical source available)
* deduplicateSessionArchive — keep most-recent 3 archived H3 blocks
- Implement appendRebuildLogSection per ADR-1817 §3 — every mutation
appends a structured entry (timestamp/kind/section/before/after/reason)
to `## Rebuild Log`. Idempotency guarantee (ADR-1817 §4): a no-mutation
rebuild appends NO log entry, so two successive runs on a clean file
are byte-identical.
Compiled output (gsd-core/bin/lib/state-transition.cjs): regenerated via
`npm run build:lib` (tsc -p tsconfig.build.json).
Tests (tests/state-rebuild.test.cjs, 18 cases):
- Dispatch + idempotency contract (3 tests, including the load-bearing
'rebuild on a clean file is a no-op' that pins §4).
- Current Position prose reconciliation, criterion #1 (3 tests).
- Template-placeholder removal, criterion #3 (3 tests).
- Session Continuity Archive de-duplication, criterion #4 (4 tests).
- **By Phase:** table reconciliation via phaseInventoryProvider, criterion
#2 (3 tests, including the Leaky-Abstractions no-op guard).
- Regression guard for sync + prune, criterion #7 (2 tests).
Verified: node --test tests/state-rebuild.test.cjs → 18/18 pass.
Verified: node --test tests/state-transition.test.cjs → 85/85 pass (no
regression on the existing 10 transitions).
Phase 2 (#1826) wires the CLI surface (cmdStateRebuild + --dry-run +
integration tests + docs + changeset). This PR adds the engine only — no
user-visible command yet, so no-changelog label applied.
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