docs: add pkg/syncutil README and register dependency in cli/workflow specs

pkg/cli/README.md

@@ -478,6 +478,7 @@ err := cli.RunHealth(cli.HealthConfig{
 - `github.com/github/gh-aw/pkg/gitutil` — Git and GitHub CLI helpers
 - `github.com/github/gh-aw/pkg/repoutil` — repository name parsing and normalization
 - `github.com/github/gh-aw/pkg/stringutil` — string manipulation and sanitization utilities
+- `github.com/github/gh-aw/pkg/syncutil` — thread-safe one-shot caching (used for repository slug lookup)
 
 **External**:
 - `github.com/spf13/cobra` — CLI framework

pkg/syncutil/README.md

@@ -0,0 +1,65 @@
+# syncutil Package
+
+The `syncutil` package provides thread-safe synchronization utilities for concurrent operations.
+
+## Overview
+
+This package provides generic types for common concurrency patterns with zero-allocation caching. It is designed for situations where an expensive or fallible operation should be executed at most once, with subsequent callers receiving the cached result.
+
+## Public API
+
+### Types
+
+| Symbol | Kind | Description |
+|--------|------|-------------|
+| `OnceLoader[T]` | struct | Caches the result of an expensive, fallible one-shot fetch; safe for concurrent use |
+
+### Methods on `OnceLoader[T]`
+
+| Method | Signature | Description |
+|--------|-----------|-------------|
+| `Get` | `func (o *OnceLoader[T]) Get(loader func() (T, error)) (T, error)` | Returns the cached result, invoking `loader` exactly once |
+| `Reset` | `func (o *OnceLoader[T]) Reset()` | Clears the cached result and error so that the next `Get` call re-invokes `loader` |
+
+## Usage Examples
+
+```go
+import "github.com/github/gh-aw/pkg/syncutil"
+
+var cache syncutil.OnceLoader[string]
+
+// loader is called only once; subsequent calls return the cached value
+value, err := cache.Get(func() (string, error) {
+    return expensiveOperation()
+})
+
+// Reset allows re-fetching the value on the next Get call
+cache.Reset()
+```
+
+**Typical usage as a package-level cache**:
+
+```go
+var currentRepoSlugCache syncutil.OnceLoader[string]
+
+func getCurrentRepoSlug() (string, error) {
+    return currentRepoSlugCache.Get(func() (string, error) {
+        return fetchRepoSlugFromGitHub()
+    })
+}
+```
+
+## Design Notes
+
+- The internal mutex ensures that `loader` is invoked at most once, even when multiple goroutines call `Get` concurrently.
+- If `loader` returns an error, the error is cached alongside the zero value of `T`; subsequent calls return the same error without re-invoking `loader`.
+- `Reset` acquires the same mutex, making it safe to call concurrently with `Get`.
+- The zero value of `OnceLoader[T]` is ready to use; no constructor is needed.
+
+## Dependencies
+
+This package has no internal or external dependencies beyond the Go standard library (`sync`).
+
+---
+
+*This specification is automatically maintained by the [spec-extractor](../../.github/workflows/spec-extractor.md) workflow.*

pkg/workflow/README.md

@@ -518,6 +518,7 @@ pkg/workflow ── FrontmatterConfig (typed structs)
 - `github.com/github/gh-aw/pkg/typeutil` — safe type conversions
 - `github.com/github/gh-aw/pkg/tty` — terminal capability detection
 - `github.com/github/gh-aw/pkg/stringutil`, `github.com/github/gh-aw/pkg/fileutil`, `github.com/github/gh-aw/pkg/gitutil`, `github.com/github/gh-aw/pkg/sliceutil` — utilities
+- `github.com/github/gh-aw/pkg/syncutil` — thread-safe one-shot caching (used for repository feature cache)
 - `github.com/github/gh-aw/pkg/types` — shared MCP types
 
 **External**: