feat: execute mixed-backend mapping and time contracts

[Brad-Edwards]

Summary

Execute admitted mixed-backend subject mappings, directed crossings, time coordination, and handoffs with correlated evidence, so runtime records distinguish accepted requests from effects, delivery, and participant observation.

Requirement UIDs

• SEM-234
• API-407

Related Issues

Refs #1355

ADR Impact

• ADR-102 (amended)

Changes

• Resolve each active edge to a versioned mapping and bridge responsibility, validate exact subjects and authorized actions, and refuse unsupported loss or time claims before invocation.
• Bind time service readback, crossing receipts, observation, handoff, partial outcomes, and restart recovery to the owning operation and immutable evidence.
• Prevent overlapping mixed action claims, add targeted regressions, and update SEM-234, API-407, ADR-102, formal contracts, and operator documentation.

Test Plan

• Unit tests pass
• Integration tests pass if applicable
• Full completion suite required in CI before merge
• No coverage regression

After synchronization with dev, 178 targeted tests passed across mixed runtime, participant crossing, and backend operation modules. The identity-policy check and mandatory pre-commit gate passed. Broad suites run in CI.

Ground Control Checks

• Repository policy checks required in CI before merge
• Pre-push Codex review completed; all findings fixed or dispositioned

Traceability

• IMPLEMENTS: SEM-234 ← implementations/python/packages/raes_runtime/mixed_runtime_edge_execution.py; implementations/python/packages/raes_runtime/mixed_runtime_recovery.py; specs/formal/participant-semantics/cross-backend-participant-control.md, API-407 ← implementations/python/packages/raes_runtime/mixed_runtime_edge.py; specs/formal/runtime-contracts/participant-backend-contracts.md
• TESTS: SEM-234 ← implementations/python/tests/test_issue_1355_mixed_mapping_time.py; implementations/python/tests/test_issue_1016_mixed_runtime_coordination.py, API-407 ← implementations/python/tests/test_issue_1355_mixed_mapping_time.py

Checklist

• Code follows the project's coding standards
• Changelog: owned by Release Please (generated from the Conventional Commit PR title; no per-PR fragment)
• Architectural docs updated if stack, package structure, or key behaviors changed

Documentation

Updated: see diff.