Retain Swift append heuristic precision blocker

[DavidBakerEffendi]

The independent Swift append control finds a false flow through a local wrong-arity extension whose body assigns a safe constant. Retain this as a precision blocker: canonical propagator qualification remains unrun and no scored configuration is activated.

Key Changes:

• Preregister and retain independent exact-identity, shipped-summary engagement, and positive/near-miss observations. Preserve the failed control and every diagnosis attempt, including a query compilation error and cache fingerprint rejection.
• Trace the false flow to native AdditionalTaintStep provenance and retain the matching shipped AppendCallStep heuristic source plus direct argument-to-receiver witnesses. Add portable integrity/mutation checks that verify the blocked evidence without promoting qualification.

Touch Points:

• adapters/codeql/swift-propagator-v1/queries/
• evidence/swift-propagator-qualification-v1/
• scripts/run-swift-propagator-control.py, scripts/trace-swift-propagator-*.py
• scripts/verify-swift-propagator-control.py, scripts/test-swift-propagator-control.py
• .github/workflows/ci.yml, .gitattributes, Swift qualification documentation

Validation: six test methods including six semantic mutations and four copied-evidence mutations passed, including from a clean Git archive; previous canonical source–sink, entrypoint, and pending integration verifiers passed; cargo fmt --check and git diff --check passed. Native control and diagnoses used preregistered 150-second extraction / 60-second query / 2048 MiB diagnostic limits. Aggregate memory compliance and semantic completeness remain unproven. CI pending.

Refs #220 and #215. Both issues remain open; acceptance is incomplete. No full-corpus run, freeze, scored activation, or publication.