enhance(#1962): harden regression tests (PBT shrinking + oracle classification + boundaries) (#2409)

* test(#1962): add failing-first repro-hardening contract tests

Epic #1957 Phase 3A. Source-text-is-the-product contract tests: PBT shrinking
(fast-check/Hypothesis, minimized seed, manual-minimization degradation), the
four oracle types (specified/derived/metamorphic/implicit with implicit flagged
weakest), boundary neighbors (off-by-one/min-max/empty-singleton tied to the
equivalence class), oracle_type in DEBUG Resolution, and the Phase 1A tie-in
(minimized seed + real oracle => the mutation guardrail bites).

Failing-first: reference, agent cross-refs, and template field do not yet exist.

* feat(#1962): harden regression tests (PBT shrinking + oracle classification + boundaries)

Epic #1957 Phase 3A. Extends Minimal Reproduction (shrinking) and Test-First
Debugging (oracle classification + boundary neighbors):
- Shrinking: wrap an input-space failing input in a property (fast-check JS/TS,
  Hypothesis Python) and store the MINIMIZED counterexample as the regression
  seed; degrade to manual minimization when no PBT framework is present.
- Oracle classification: state specified / derived (contract/model) /
  metamorphic / implicit (crash, weakest) before writing the assertion; record
  under Resolution.oracle_type; never default to implicit silently.
- Boundary neighbors: off-by-one, min/max, empty/singleton around the fixed
  defect's equivalence class.

Together they turn the regression test into a root-cause check — what the Phase
1A mutation guardrail needs to bite. Full rules extracted to gsd-core/references/
debugger-repro-hardening.md. INVENTORY + manifest + agent-size baseline +
install-parity goldens + AGENTS.md + DEBUG template updated.

* fix(#1962): address orthogonal review (bounding, provenance, oracle scope, sufficient-triple)

- HIGH: added a 'Bound the property/shrink run' section (60s timeout, degrade-
  to-manual on timeout, do-not-raise-default-run-limits, argv-not-shell) —
  the gauntlet violation the sibling references already honored.
- Medium: test-provenance caveat (the failing input often comes from the bug
  report — author the generator from a sanitized description, cross-ref
  debugger-fix-acceptance.md).
- Medium: oracle scope note — the 4 types cover deterministic bugs; non-
  deterministic failures re-route to stability-stress per bug-taxonomy.
- Medium: Phase 1A tie-in corrected — seed+oracle is necessary not sufficient;
  boundary neighbors close the adjacent-input escape; the sufficient triple is
  seed+oracle+neighbors.
- Low: preserve the original noisy repro as a secondary reference; operationalize
  'equivalence class' (the predicate the fix draws). Nit: degradation reworded.

* chore(#1962): backfill changeset pr number (PR #2409)

---------

Co-authored-by: sim <sim@local>

tests/fixtures/golden-install-parity/codebuddy.json

@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "5342fcc0da974696",
   "agents/gsd-codebase-mapper.md": "b995bf01af0193d2",
   "agents/gsd-debug-session-manager.md": "9f56455afb580275",
-  "agents/gsd-debugger.md": "eda03be2187625f8",
+  "agents/gsd-debugger.md": "0dd86ecf4e9e3ee9",
   "agents/gsd-doc-classifier.md": "c2bf59af9467810b",
   "agents/gsd-doc-synthesizer.md": "b2a179bf3c9bd636",
   "agents/gsd-doc-verifier.md": "e74d930905a782ea",
@@ -135,6 +135,7 @@
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "16f0cb55eb457f33",
   "gsd-core/references/debugger-rca-branching.md": "7dcf3ddbe3591250",
+  "gsd-core/references/debugger-repro-hardening.md": "fdf55a6cee9b1792",
   "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
@@ -226,7 +227,7 @@
   "gsd-core/references/worktree-branch-check.md": "21d9c31bf6542b93",
   "gsd-core/references/worktree-path-safety.md": "3c8d74756f9b16a8",
   "gsd-core/templates/AI-SPEC.md": "efa1f8354bd3a24b",
-  "gsd-core/templates/DEBUG.md": "bd6a1beccdae67dc",
+  "gsd-core/templates/DEBUG.md": "c8768312f4c1e438",
   "gsd-core/templates/README.md": "93d3426fc64e2c12",
   "gsd-core/templates/SECURITY.md": "b628f7f1c6d2328f",
   "gsd-core/templates/UAT.md": "9e296471b97ebcec",