27f5f84e3b
- Fix two root-AGENTS.md cross-links that the depth bump left pointing at the new docs/AGENTS.md instead of the root file they cite (capability-seams, optional-code-mode). These resolved on disk so verify-md-links passed — the gate checks existence, not which file you meant; corrected to ../../../. - Broaden verify-md-links scope to .agents/skills/**/*.md: this PR rewrote the dsh-code-review skill's links into the RFC tree, but the skill dir was outside the gate, so a broken skill link would have passed silently. - Percent-decode the path component before the existence check, so a valid encoded relative target (My%20File.md) is not falsely reported broken; a malformed escape (%zz) is reported broken rather than crashing the gate. - Drop the merged property-testing RFC's "nightly CI job 100x" claim: that line came from the original proposal, not the accepted decision, and CI has only push/pull_request triggers — note it as possible future work instead. doc-sync (incl. verify-md-links over 58 files), doc-typecheck, lint pass.
28 lines
3.3 KiB
Markdown
28 lines
3.3 KiB
Markdown
# RFC: Property-based testing for protocol-shaped code
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Status: implemented (proposed 2026-06-11, accepted 2026-06-14)
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<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
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> Merges the original proposal and the decision record for one topic. It found a real BlockAssembler duplicate-`block-end` bug on first run.
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## Context
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Example-based tests pin the cases we thought of. The harness's core is protocol-shaped — chunk streams, event logs, schema conversion, inbox scheduling — where the input space is combinatorial and the interesting bugs live in interleavings nobody wrote an example for. The motivating evidence: a `streamBlocks` ordering bug once survived 100% line coverage of the happy paths. Per-file 100% coverage proves every line ran, not that every interleaving is correct.
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## Decision
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Adopt `fast-check` (a root devDependency) with one `tests/properties.spec.ts` per protocol-shaped package, generators tuned for *realistic-but-adversarial* inputs (not uniform noise) and `numRuns` kept so the suite stays well under ~10s locally. Failures print a reproducible seed. (The original proposal also sketched a nightly CI job running 100× the iterations; that was not shipped — the property suite runs only in the normal `push`/`pull_request` CI, and a scheduled high-iteration job remains possible future work.)
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- **dsh-llm / BlockAssembler:** arbitrary chunk streams (valid + malformed: duplicate indices, stragglers, missing block-start). Invariants: `flushReady()+flushRemaining() ≡ blocks()` in order; the streamed prefix is always a prefix of final `blocks()`; partial count ≤ distinct indices; re-assembly idempotent.
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- **dsh-session:** arbitrary event logs. Invariants: `deriveMessages` deterministic; replay-from-seed identical; seq strictly monotonic; non-message events never affect derived history; derived content is decoupled from the log.
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- **dsh-tools:** arbitrary `SchemaSpec`. Invariants: JSON Schema `required` equals the `required:true` keys at every level; conversion total; **and the composition with [runtime arg validation](2026-06-11-runtime-arg-validation.md)** — generated args satisfying a spec pass `validateArgs`, and targeted corruptions (dropped required key, non-object top level) are rejected. This closes the validator/`InferArgs` drift risk.
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- **dsh-agent-loop:** arbitrary send schedules against a never-exhausting adapter, driven through the `agent/status` settle signal (no wall-clock sleeps). Invariants: no message lost; turn numbers strictly increase; status transitions stay on the legal machine.
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## Consequences
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- Generator quality is the value lever — the generators bias toward small index pools and short strings so collisions and interleavings are common.
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- **It already paid off:** the BlockAssembler stream found a real bug — a duplicate `block-end` at the same index overwrote an already-flushed block, so the streamed prefix disagreed with final `blocks()`. Fixed (first close wins, matching the existing straggler rule) with a dedicated regression test.
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- A property flake from a timeout is a finding, not something to retry away. The loop properties are deterministic by construction (settle on `agent/status`), so a hang is a real defect.
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- Property tests supplement, not replace, the example tests that pin specific branches for the 100%-coverage gate.
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