Fix Reason error format and update AGENTS.md with gating checks

Change error messages in Reason.Validate() and Reason.MarshalJSON()
to use %d instead of %q. Reason is an integer type, and %q prints the
value as a rune character rather than its integer representation, making
the error message misleading.

Add a dedicated "Gating Checks" section to AGENTS.md that lists the
three mandatory pre-submit commands: gofmt, go test, and golangci-lint.
Remove the now-redundant guidelines that mentioned running tests and
following Go conventions, and merge the remaining numbered list.

Author: maruel

AGENTS.md

@@ -12,6 +12,14 @@
   - It installs `cmd/list-models` and `cmd/scoreboard`, writes `docs/MODELS.md`, then runs `go generate ./...`.
   - If a provider fails after the env check, inspect the `list-models -strict -provider <provider>` error. The script deletes that provider's `Warmup.yaml` and runs `go test ./providers/<provider>/...` to expose stale recording issues. Never use `RECORD=all`.
 
+## Gating Checks
+
+Before submitting changes, run:
+
+1. `gofmt -w -s .`
+2. `go test ./...`
+3. `golangci-lint run ./...`
+
 ## Directory Structure
 
 - Shared client implementation: `base/`
@@ -165,9 +173,7 @@ func (o *Options) Validate() error {
 1. **Before making changes**: Understand the existing patterns and conventions
 2. **Write tests first**: Test-driven development is preferred
 3. **Update documentation**: Keep README.md and code comments current
-4. **Run the full test suite**: Ensure all tests pass before submitting
-5. **Follow Go conventions**: Use `gofmt`, `golint`, `go vet -vettool=shadow`, `staticcheck` and `gosec`
-6. **Add examples**: Include usage examples for new features
+4. **Add examples**: Include usage examples for new features
 
 ---
 

scoreboard/scoreboard.go

@@ -383,7 +383,7 @@ func (t Reason) Validate() error {
 	case ReasonNone, ReasonInline, ReasonAuto:
 		return nil
 	default:
-		return fmt.Errorf("invalid Reason: %q", t)
+		return fmt.Errorf("invalid Reason: %d", t)
 	}
 }
 
@@ -398,7 +398,7 @@ func (t Reason) MarshalJSON() ([]byte, error) {
 	case ReasonAuto:
 		return []byte(`"auto"`), nil
 	default:
-		return nil, fmt.Errorf("invalid Reason: %q", t)
+		return nil, fmt.Errorf("invalid Reason: %d", t)
 	}
 }