Schema-enforce atlas leaf-dispatch via write-fragment CLI + JSON Schema derivation

[jpr5]

Summary

Phase-0 implementation of atlas leaf-schema enforcement (per spec Notion 37d3aa38185281a686bbc46671a63a42, plan at /tmp/specs/2026-06-12-atlas-leaf-schema-enforcement-impl-plan.md).

• canonicalizeFragment utility for shadow-gate dual-run comparison (recursive key sort, whitespace normalization, numeric canonicalization).
• EpisodicCandidateFragmentSchema: narrowed schema on top of CandidateFragmentSchema with sensitivity-floor transform (public → internal) and 4 episodic invariants (needsReview === true, provenance_class === "derived", confidence === "low", validation_status === "unverified").
• JSON Schema derivation via zod-to-json-schema (CANDIDATE_FRAGMENT_JSON_SCHEMA, EPISODIC_CANDIDATE_FRAGMENT_JSON_SCHEMA, jsonSchemaForFamily()).
• atlas harvest write-fragment --stdin CLI: spec §4.2.1 0/1/2/3/4 exit-code matrix, --stem filesystem-safe regex gate, mkdir/write try-block split, AND-case precedence on episodic invariant routing.
• Dual-run scaffold (runDualRun): seed-present strict / no-seed-relaxed / both-malformed-gated branches with shape XOR + both-missing → diverge guards across classification enums, sourcetype, evidence, and text fields.
• Tests: 7 new test files covering canonicalize, episodic schema, JSON schema, defect-regression corpus (14 alias rows + 12 row mutators), refinement-coverage, dual-run, write-fragment CLI.

Test plan

• Full vitest: 6176/6176 passing, 338/338 test files
• TypeScript build clean
• Prettier clean
• 7-round cr-loop converged (49 review agent passes; agent-confirmed zero findings on round 7)
• CI green (pending)

Notes

• Deferred follow-ups (see /tmp/cr/atlas-leaf-schema-r*-TRIAGE.md for full bundle): Phase-2 dual-run cosine + DI signature; JSON-Schema-layer ajv test hardening (T7/T3/T9); CLI ergonomics (--stem empty-string; --runs-dir env default; --fragment-id spec footer-note); atomic write temp+fsync+rename; README exit-code matrix subtlety; type-design polish.

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