chore(release): complete v1.9.7 migration and compatibility rehearsal

Purpose

Turn the roadmap's 1.9.7 migration claims into executable, archive-owned evidence while preserving the frozen 1.9 public interface.

Change boundary

• Add two all-domain consumer projects and one focused alias/package consumer.
• Add a standard-library Python contract validator/checker and regression tests.
• Publish the machine-readable rehearsal, human migration guide, external conceptual mappings, and final alias decision list.
• Integrate the checker into CI and release qualification.
• Advance release identity and current documentation to 1.9.7.
• Do not change a src/*.pas interface or implementation, add a dependency, introduce a compatibility package, or copy third-party numerical code.

Decisions

1. Retain all four pressure/velocity aliases in place. The rehearsal proves they are exact, useful focused imports with no hidden package dependency; visual consolidation alone is not a deprecation reason. 2. Keep candidate-2.0 examples on declarations already shipped in 1.9.7. They demonstrate conventions, not an unreleased binary surface. 3. Describe NumLib and LMath/DMath mappings at the mathematical/task level and require semantic-difference plus unsupported-case notes for every mapping. 4. Store stable claims in migration-rehearsal-1.9.7.json and host/compiler observations in generated qualification output.

Review focus

• Correctness: consumers assert results, diagnostics, alias identity, clone/ ownership behavior, zero-based indexing, and deterministic replay.
• Architecture: migration tooling remains outside the numerical runtime; the main package retains its existing unit set and sole FCL dependency.
• Security: external mappings are documentation only; the checker reads local JSON/XML as untrusted structured data and runs no downloaded code.
• Performance: release runtime paths are unchanged; rehearsal programs are bounded and compile only during validation.
• Documentation: API decision data, generated reference, domain guide, changelog, README, support/releasing guidance, and roadmap agree.

Verification

python tools/test_migration_rehearsal.py

python tools/check_migration_rehearsal.py --compiler fpc

python tools/test_api_decision.py

python tools/check_api_decision.py

lazbuild --build-all packages/lazarus/mathlib_fp.lpk

The complete release gate is:

python tools/qualify_release.py --release 1.9.7 --compiler fpc \

  --lazbuild lazbuild