react-spa generator oracle-coverage parity (match react-native)

[artyhoo]

Summary

Stage 1 of #646 ships two curated presets — preset-react-spa and preset-react-native. Stage 2 (stage-2-generate-path, #691) gave react-native a stub-driven generate-path oracle-coverage test, but react-spa has none. The hand-authored preset-react-spa/eslint-rules/require-error-boundary.ts has never been run through the synthesize → L4 → emit pipeline, even at stub level. This issue closes that asymmetry.

Grounded current state (verified against staging 2026-06-26)

• react-native — covered. packages/core/synthesizer/generate.test.ts exercises a recipe-less RN ResearchPlan (fixtures/rn-research-plan.json) through synthesizeGenerate(...) and asserts: (a) L4 accepts, (b) the emitted rule set fires (FlatList → FlashList), (c) oracle coverage against RULES.react-native.md (IDs R12/R14/R15/R18). The LLM GenerateClient is a deterministic stub (generate-stubs.ts:stubGenerateRN, "test use only") — so this proves the pipeline handles RN's documented rule set, not that a live LLM reproduces it (live Path A is non-deterministic and tested separately).
• react-spa — not covered. No react-spa fixture, no stubGenerateReactSPA, no oracle-coverage test against RULES.react-spa.md. grep -rn 'react-spa' packages/core/synthesizer/*.test.ts fixtures/ → empty.

Why it was deferred (not a bug)

Stage 2 acceptance required only "≥1 proving-case stack" (stage-2-generate-path/kickoff.md:66). react-native (4-rule set) satisfied the ≥1 floor; react-spa (single gap rule require-error-boundary) was a listed candidate but not required once RN was exercised. The result is a silent asymmetry — exactly the "stranded hand-maintained preset" failure README §Methodology warns about: one Stage-1 preset is generator-pipeline-covered, the other is hand-only.

Scope (small — NOT an epic)

Mirror the RN treatment for react-spa:

1. Add a frozen fixtures/react-spa-research-plan.json (oracle = RULES.react-spa.md).
2. Add stubGenerateReactSPA to generate-stubs.ts returning the react-spa rule set (require-error-boundary + any plugin-sourced rules).
3. Add a generate.test.ts block (or sibling test) asserting: L4 accepts the plan; require-error-boundary fires on a paired bad/good fixture; emitted set covers every RULES.react-spa.md oracle ID.

Estimated ~1–2 h. Each new rule/fixture follows principle 02 (paired negative) and the existing capability-commit discipline.

Out of scope

• Live-LLM proof of Path A (non-deterministic; not unit-tested — same boundary as RN).
• Path B (LLM authors AST source), Gate 3 (Stryker), Gate 5 (two-AI review) — their own deferred triggers per open-questions.md §13.10 areas 3/4/5.

Acceptance criteria

• A react-spa generate-path test exists and is green; covers all RULES.react-spa.md oracle IDs (parity with the RN test's T7 oracle-coverage block).
• make self-audit stays green.

Context

• Parent: Multi-stack support — React/React Native now (Stage 1), any detected stack via L2 research (Stage 2) #646 (closed) — Stage 1 presets + Stage 2 generate-path.
• Template to mirror: packages/core/synthesizer/generate.test.ts (RN oracle-coverage), generate-stubs.ts:stubGenerateRN.

[artyhoo]

Oracle confirmed (verified against staging 2026-06-26)

RULES.react-spa.md:15-18 — the react-spa oracle is 3 IDs, of which only one is a custom BUILD rule:

Oracle ID	Source	Generate-test coverage shape (mirror RN)
R-SPA-EB (error-boundary)	custom AST rule eslint-rules/require-error-boundary.ts (BUILD, SSOT #140)	L4-validated rule — fires on missing ErrorBoundary ancestor / clean when present (paired fixture)
R-SPA-A11Y	eslint-plugin-jsx-a11y (ADOPT)	plugin-sourced — "manual" coverage (like RN R14/R15, not in L4 KNOWN_PLUGINS)
R-SPA-HOOKS	eslint-plugin-react-hooks@^6 (ADOPT)	plugin-sourced — "manual" coverage

So this is a near-mirror of the RN generate-test (RN = 4 oracle IDs, 2 custom). The earlier "first step: read the oracle" caveat is now discharged — the ~1-2 h estimate holds. Only R-SPA-EB needs a real L4-validated stub-generated rule + paired fixture; the other two assert plugin presence.