[IR-P1][WS1] Phase 1 Build IR core and compiler (epic)

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Problem statement

Phase 1 needs a controlling epic to coordinate deliverables, acceptance criteria, and traceability for Build IR core and compiler.

Intended invariant

Introduce a Rust-owned IR crate and compile Python model metadata into deterministic IR artifacts.

Scope boundaries

• Coordinates Phase 1 roadmap scope only
• Tracks delivery issues and phase exit gate evidence
• Defers unrelated feature expansion outside IR roadmap scope

Deliverable checklist

• Sub-issues for all phase deliverables are opened and linked
• Phase deliverables are implemented and verified
• Deterministic SchemaIR serialization + model-set fingerprinting verified in CI
• Representative model IR snapshots are stable in CI
• No user-visible behavior changes confirmed across Phase 1 deliverables
• Exit gate evidence is linked in roadmap and issues
• Migration and docs impact fields are kept synchronized

Validation plan

Phase 1 closes only when linked sub-issues are complete and roadmap phase exit gates are satisfied with evidence.

Rollback/failure mode

If scope expands or deliverables split, create follow-up issues and update roadmap + issue links in the same work session.

Roadmap reference

Roadmap reference: docs/plans/2026-06-19-001-ir-first-roadmap.md (Phase 1)

Migration impact

none - phase-level impact estimate; refine on each sub-issue.

Documentation impact

update-existing - phase requires synchronized docs updates with implementation.

Sync status

Synced with roadmap: 2026-06-19 (Phase 1 implementation evidence linked in roadmap and migration guide on working branch)

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Phase sub-issues:

• [IR-P1][WS1] Add ferro-schema-ir crate with versioned serde types #77 Add ferro-schema-ir crate with versioned serde types
• [IR-P1][WS1] Add Python -> SchemaIR compiler path #78 Add Python -> SchemaIR compiler path
• [IR-P1][WS1] Persist IR hashing and CI snapshots #79 Persist IR hashing and CI snapshots

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Closing as completed by PR #104 (Phase 1 IR core + compiler).