[rig-sampler] Add s.literal helper for single-value enum constraints

[github-actions]

Sample run

Ran sample 14-changelog-categorizer.ts (a validation-plan agent) through the stub harness. The agent produced valid JSON in 1 turn with no repair. Output schema used s.array(s.string) for commands and manualChecks, and s.string for rationale.

What the run revealed

The schema helpers are well-used in samples, and enum-based constraint is a recurring pattern. However, when a field must be exactly one specific value (e.g. a "done" status sentinel or a fixed protocol token), authors must write s.enum("done") — which works but doesn't clearly signal "single literal" intent. It can also be confused with "one of many choices".

Change

Added s.literal<T>(value: T, description?: string): EnumSchema<[T]> to the s helpers:

s.literal("done")               // accepts only "done"; infers as "done"
s.literal(42)                   // accepts only 42; infers as 42
s.literal(true, "must be true") // with description

• Implemented as a thin wrapper around the existing EnumSchema/serializeSchema path (no new logic).
• Inferred TypeScript type is the narrow literal T, not a union.
• Documented with JSDoc + examples in rig.ts.
• Header summary line updated.
• 5 new unit tests added in src/rig.test.ts covering serialization, validation (pass/fail), and description propagation.
• All 141 existing tests continue to pass.

Generated by Daily Rig Sampler · 86.5 AIC · ⌖ 8.21 AIC · ⊞ 5.2K · ◷

[github-actions]

🧠 Matt Pocock Skills Reviewer has completed the skills-based review. ✅

[github-actions]

Skills-Based Review

Applied /tdd - approving with one non-blocking suggestion on test duplication.

• Minor test duplication: the 'converts literal schemas' case in the toJsonSchema block repeats three assertions already in the new s.literal suite. Low risk but worth cleaning.

Positive highlights:

• Clean thin-wrapper, no new logic, delegates to existing EnumSchema path
• const T generic correctly narrows the inferred type to the literal
• Tests cover serialization, validation accept/reject, and description propagation
• JSDoc examples and header summary updated

🧠 Reviewed using Matt Pocock's skills by Matt Pocock Skills Reviewer · 27.2 AIC · ⌖ 5.76 AIC · ⊞ 6.3K
_{Comment /matt to run again}

[github-actions]

[/tdd] These three assertions duplicate the ones in the new s.literal describe block below (lines ~1186–1219). Keeping them in both places will cause drift if the behaviour changes.

💡 Suggestion

Remove this "converts literal schemas" test case from the toJsonSchema describe block entirely — the dedicated s.literal suite already covers serialization exhaustively. Alternatively, replace the three expects with a single representative assert here and add a comment pointing to the full suite.