fix(credentials-local): one operation chain, read-modify-write under the shared writer lock, and a quote-aware line editor

Review round three, credentials half. dsh-atomic-write grows the
cross-process writer-lock primitive (withFileLock: wx sentinel, bounded
backoff, stale takeover via onStaleBreak, deadline failure) plus a dirMode
option, and settings-local migrates its private copy to it; both providers
now create harness-home directories 0700.

credentials-local reuses the reviewed settings-local shape: watcher
reloads and line edits share one settled operation chain; every write
re-reads the document under the lock and publishes unobserved external
entries before editing, so an edit inside the debounce window (or another
process's write) can never be overwritten; the watcher's ready signal
queues one reconcile closing the startup gap.

The line editor is now physical-line aware: continuation lines of a
quoted multi-line value are never mistaken for assignments, untouched
lines keep their exact bytes (CRLF included), an edited line keeps its
own terminator, and appends use the document's dominant ending. A
multi-line entry reports writable: false, matching what set() would do.

The Credentials base class owns a contained notifyUpdated fan-out:
providers publish only after the commit, every listener runs, sync throws
and async rejections are logged without failing the committed write, and
INVARIANT-coded failures rethrow after the fan-out.

packages/credentials/credentials/src/index.ts

@@ -55,7 +55,12 @@ declare module 'cordis' {
     /**
      * Committed change to a provider-managed credential source: a `set`, an
      * `unset`, or an external edit observed in storage. Ambient
-     * process-environment changes are not observable and never emit.
+     * process-environment changes are not observable and never emit. Listener
+     * failures are contained and logged — a sync throw and an async rejection
+     * alike — without changing the committed operation's outcome, except
+     * `INVARIANT`-coded failures, which rethrow after every listener ran;
+     * that rethrow reaches the emitter only from synchronous listeners, so
+     * invariant checks on this event must not be async functions.
      * @param ref - the reference whose stored value changed.
      * @mode emit
      */
@@ -109,6 +114,49 @@ export abstract class Credentials extends Service {
    * @param ref - the reference to remove.
    */
   abstract unset(ref: CredentialRef): Promise<void>
+
+  /* jscpd:ignore-start -- deliberate symmetry with the settings seam's commit
+     fan-out: the contained-dispatch shape is the reviewed listener-lifecycle
+     contract, and extracting it would couple the two seams' event semantics. */
+  /**
+   * Fan `credentials/updated` out with contained listener failures: every
+   * listener runs, and a sync throw or async rejection is logged without
+   * changing the committed operation's outcome — except `INVARIANT`-coded
+   * failures, which rethrow after every listener ran (the rethrow reaches the
+   * caller only from synchronous listeners, so invariant checks on this event
+   * must not be async functions). Providers call this only after the write or
+   * reload actually committed, so a broken observer can never make a durable
+   * change look failed.
+   * @param ref - the reference whose stored value changed.
+   */
+  protected notifyUpdated(ref: CredentialRef): void {
+    let invariantFailure: unknown
+    const args = ['credentials/updated', ref]
+    for (const listener of this.ctx.events.dispatch('emit', args) as Array<(...listenerArgs: unknown[]) => unknown>) {
+      try {
+        const returned = listener(ref)
+        if (returned != null && typeof (returned as PromiseLike<unknown>).then === 'function') {
+          void Promise.resolve(returned as PromiseLike<unknown>).then(undefined, (error: unknown) => {
+            this.warnListenerFailure(ref, error)
+          })
+        }
+      } catch (error) {
+        if ((error as { code?: unknown } | null)?.code === 'INVARIANT') {
+          invariantFailure ??= error
+          continue
+        }
+        this.warnListenerFailure(ref, error)
+      }
+    }
+    if (invariantFailure !== undefined) throw invariantFailure as Error
+  }
+  /* jscpd:ignore-end */
+
+  /** Contained-listener diagnostic shared by the sync and async failure paths. */
+  private warnListenerFailure(ref: CredentialRef, error: unknown): void {
+    this.ctx.logger.warn('credentials: a credentials/updated listener for "%s" failed', ref)
+    this.ctx.logger.warn(error)
+  }
 }
 
 export default Credentials