[IR-P7][WS6] Ship public IR-first upgrade with deprecated paths still supported

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Problem statement

Phase 7 deliverable 1 needs a dedicated issue to ship the public IR-first upgrade while preserving deprecated compatibility paths.

Intended invariant

Public release is available without removing deprecated methods yet; warnings point users to v0.13.0 removal.

Scope boundaries

• Implements only this Phase 7 deliverable
• Keeps compatibility paths available
• Defers compatibility-path removal to Phase 8

Deliverable checklist

• Implementation complete for this deliverable
• Tests added/updated and passing
• Migration impact recorded with rationale
• Docs impact recorded with required updates landed
• Evidence linked for roadmap phase gate

Validation plan

Define and execute deterministic tests for this deliverable; attach verification evidence before closing.

Parent epic

#100

Roadmap reference

Roadmap reference: docs/plans/2026-06-19-001-ir-first-roadmap.md (Phase 7)

Migration impact

minor - release introduces/continues deprecation warnings but keeps compatibility paths available.

Documentation impact

update-existing - release + compatibility-window docs require updates.

Sync status

Synced with roadmap: 2026-06-19