[rig-sampler] feat(validation): improve missing-field error descriptions for constrained string schemas

[github-actions]

Samples run

Five consecutive samples were run through the stub Copilot SDK runner (npm run sample):

Sample	Result	Notes
57-complex-integration-sonnet.ts	✅ pass	Complex schema with s.enum("low","medium","high") for riskLevel, s.optional(s.string) for audience, multi-agent delegation, and tools. All fields conformed on first turn.
58-async-tool-node-builtins.ts	✅ pass	Uses s.string for pid and s.enum("running","idle","unknown") for status. Exposed that s.string in missing-field errors gives no hint about expected format.
59-bash-each.ts	✅ pass	Uses s.url in the input array endpoints; a missing url field would only report "expected string" — unhelpful when the model should know it needs a URI.
01-single-agent-haiku.ts	✅ pass	Simple baseline; no constrained strings.
02-review-git-diff.ts	✅ pass	Uses s.optional(s.number) for line; plain strings elsewhere.

What the runs revealed

• Samples 57–59 all define schemas using constrained string helpers (s.url, s.nonEmptyString, s.path, s.date).
• When a required field of one of these types is missing, the repair prompt previously said "missing required field (expected string)" — the same message for s.string, s.nonEmptyString, s.url, s.path, and s.date.
• This forces the model to infer constraints from context rather than from the error itself, which can lead to unnecessary repair turns.

The improvement

describeSchemaType (used only in missing-field error messages) now returns a specific label for constrained string schemas:

Schema helper	Before	After
s.nonEmptyString	"string"	"non-empty string"
s.url	"string"	"URL string"
s.date	"string"	"date string (YYYY-MM-DD)"
s.path	"string"	"path string"
s.string	"string"	"string" (unchanged)

This is a non-breaking, internal-only change: describeSchemaType is a private helper, and the public ValidationResult type is unchanged. Four new unit tests cover the new messages.

Generated by Daily Rig Sampler · sonnet46 91.5 AIC · ⌖ 8.3 AIC · ⊞ 5.4K · ◷

[github-actions]

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

[github-actions]

Skills-Based Review 🧠

Applied /tdd and /grill-with-docs — approving. The change is focused, well-motivated, and fully covered by tests.

📋 Key Themes & Highlights

Positive Highlights

• ✅ Four unit tests — one per constrained type — match the four new code branches exactly
• ✅ format checks take precedence over minLength, matching the specificity hierarchy of the schema helpers
• ✅ Non-breaking: describeSchemaType is private; ValidationResult public surface unchanged
• ✅ PR body includes a clear before/after table grounded in real sampler runs

Minor Observations

• The minLength > 0 guard is redundant given that s.nonEmptyString always sets minLength: 1, but it makes the intent explicit and causes no harm.
• No existing test covers a schema with both format and minLength set simultaneously (not a real helper today). Low risk given the private scope.

🧠 Reviewed using Matt Pocock's skills by Matt Pocock Skills Reviewer · sonnet46 27.4 AIC · ⌖ 5.98 AIC · ⊞ 6.3K
_{Comment /matt to run again}