docs: initial conventions from cockroachdb/cockroach

Key patterns: stopper handle, errors.Wrap, TODO(owner), 116 4-file packages,
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conventions.md

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+# Patterns Extracted from cockroachdb/cockroach
+
+## Pattern: Stopper for Goroutine Lifecycle
+
+**Source:** `pkg/util/stop/stopper.go`
+**Category:** concurrency
+
+**What:** A dedicated struct that manages the lifecycle of
+all goroutines in a component: tracks active tasks, refuses
+new work during shutdown (quiesce), waits for completion,
+then runs closers.
+
+**Why:** In distributed systems, clean shutdown is critical.
+You need to: (1) stop accepting new work, (2) finish
+in-flight work, (3) release resources in order. The Stopper
+centralizes this instead of scattering shutdown logic across
+every goroutine.
+
+**Example:**
+
+```go
+type Stopper struct {
+    quiescer chan struct{} // closed when quiescing
+    stopped  chan struct{} // closed when fully stopped
+    mu struct {
+        syncutil.RWMutex
+        _numTasks int32
+        quiescing, stopping bool
+        closers []Closer
+    }
+}
+
+// RunAsyncTask refuses new work during quiesce
+func (s *Stopper) RunAsyncTask(ctx context.Context,
+    taskName string, f func(context.Context)) error {
+    if !s.addTask() {
+        return ErrUnavailable
+    }
+    go func() {
+        defer s.decTask()
+        f(ctx)
+    }()
+    return nil
+}
+```
+
+**When to use:** Any server or subsystem that spawns
+goroutines and needs graceful shutdown. Especially in
+long-running services where leaked goroutines cause
+resource exhaustion.
+
+**When NOT to use:** Simple programs with a single main
+goroutine. Or when `errgroup` with context cancellation
+suffices for the shutdown coordination.
+
+---
+
+## Pattern: Tracked Lifecycle with Leak Detection
+
+**Source:** `pkg/util/stop/stopper.go`
+**Category:** testing
+
+**What:** Register every Stopper instance in a global
+tracker. In tests, call `PrintLeakedStoppers(t)` to detect
+any Stopper that was created but never stopped — indicating
+a resource leak.
+
+**Why:** Distributed systems have complex lifecycle graphs.
+A forgot-to-stop bug silently leaks goroutines and
+connections. The tracker makes leaks fail-loud in tests
+without requiring careful manual cleanup.
+
+**Example:**
+
+```go
+var trackedStoppers struct {
+    syncutil.Mutex
+    stoppers []stopperWithStack
+}
+
+func register(s *Stopper) {
+    trackedStoppers.Lock()
+    trackedStoppers.stoppers = append(...)
+    trackedStoppers.Unlock()
+}
+
+func PrintLeakedStoppers(t testing.TB) {
+    for _, tracked := range trackedStoppers.stoppers {
+        t.Errorf("leaked stopper, created at:\n%s",
+            tracked.createdAt)
+    }
+}
+```
+
+**When to use:** Any resource that must be explicitly
+closed/stopped and where forgetting to do so causes silent
+degradation.
+
+**When NOT to use:** Resources with finalizers or GC-safe
+cleanup. Adds global state — only for testing.
+
+---
+
+## Pattern: Quiesce Then Stop (Two-Phase Shutdown)
+
+**Source:** `pkg/util/stop/stopper.go`
+**Category:** concurrency
+
+**What:** Shutdown has two explicit phases: (1) Quiesce —
+refuse new work, wait for in-flight to finish; (2) Stop —
+run closers, signal done. Components observe
+`ShouldQuiesce` channel alongside context.
+
+**Why:** One-phase shutdown (just cancel context) loses
+in-flight work. Two-phase gives running tasks time to
+complete while preventing new work from starting. The
+explicit channel (vs just context) lets components
+distinguish "winding down" from "dead."
+
+**Example:**
+
+```go
+func worker(s *Stopper, ctx context.Context) {
+    for {
+        select {
+        case <-s.ShouldQuiesce():
+            return // graceful: finish current, exit
+        case <-ctx.Done():
+            return // hard cancel
+        case work := <-workChan:
+            process(work)
+        }
+    }
+}
+```
+
+**When to use:** Servers handling requests where you want
+zero-downtime deploys (drain then stop). Load balancers,
+RPC servers, queue consumers.
+
+**When NOT to use:** Batch jobs or CLIs where immediate
+exit is fine.
+
+---
+
+## Pattern: CloserFn Adapter
+
+**Source:** `pkg/util/stop/stopper.go`
+**Category:** concurrency
+
+**What:** Define a `Closer` interface with one method
+(`Close()`), plus a `CloserFn` type that adapts any
+function into a Closer.
+
+**Why:** The adapter pattern (like `http.HandlerFunc`)
+avoids forcing users to define a struct just to implement
+a one-method interface. Cleanup functions can be registered
+directly.
+
+**Example:**
+
+```go
+type Closer interface { Close() }
+type CloserFn func()
+func (f CloserFn) Close() { f() }
+
+// Usage:
+stopper.AddCloser(stop.CloserFn(func() {
+    conn.Close()
+}))
+```
+
+**When to use:** Any one-method interface where callers
+often have a simple function they want to register.
+
+**When NOT to use:** Interfaces with >1 method, or when
+the implementation needs state beyond a closure.
+
+<!-- PATTERN_COMPLETE -->