fix: scan only subschema positions, await stderr, show the whole report

Copilot review round 6.

- Share one traversal between `walk` and `declaresAnyId`. The `$id` guard
  added last round descended through EVERY object value, including
  instance data — `examples: [{"$id": "x"}]`, a `default`, a `const` —
  where `$id` is a payload key declaring no embedded resource. Reading
  one there suppressed `remote-ref` for the whole document, turning last
  round's false-positive fix into a blanket false negative. Both passes
  now go through `forEachSubschema`, driven by the same keyword tables,
  so they cannot drift about what counts as a schema position.

- Await the stderr writes. `writeSchemaLintReport` used a bare
  `process.stderr.write`, but both CLI exit paths call `process.exit()`
  as soon as the work returns, which discards anything still buffered on
  a piped stderr — truncating or losing the multi-block `--strict`
  report on exactly the redirected-output runs a CI caller uses. Added
  `awaitableError` beside the existing `awaitableLog` and awaited it.
  The test's fake defers its callback so a synchronous one cannot make
  the assertion vacuous; two existing stderr stubs that never invoked
  their callbacks were fixed in the same pass.

- Show the CLI README's sample report in full. It printed one error
  block immediately followed by the summary, a shape the formatter
  cannot produce — every finding gets a block. Captured from a real run.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UL9retfvAXRgvi6EWk4SY4
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/cli/__tests__/schema-lint-report.test.ts

@@ -61,8 +61,11 @@ describe("writeSchemaLintReport", () => {
   beforeEach(() => {
     stderr = "";
     originalWrite = process.stderr.write;
-    process.stderr.write = ((chunk: unknown): boolean => {
+    process.stderr.write = ((chunk: unknown, ...rest: unknown[]): boolean => {
       stderr += typeof chunk === "string" ? chunk : String(chunk);
+      (
+        rest.find((r) => typeof r === "function") as (() => void) | undefined
+      )?.();
       return true;
     }) as typeof process.stderr.write;
   });
@@ -71,24 +74,46 @@ describe("writeSchemaLintReport", () => {
     process.stderr.write = originalWrite;
   });
 
-  it("writes nothing at all when there are no findings", () => {
-    writeSchemaLintReport([], true);
+  it("writes nothing at all when there are no findings", async () => {
+    await writeSchemaLintReport([], true);
     expect(stderr).toBe("");
   });
 
-  it("writes a one-line hint without --strict", () => {
-    writeSchemaLintReport(lintListResult(DIRTY_LIST), false);
+  it("writes a one-line hint without --strict", async () => {
+    await writeSchemaLintReport(lintListResult(DIRTY_LIST), false);
     expect(stderr.trimEnd().split("\n")).toHaveLength(1);
     expect(stderr).toContain("Re-run with --strict");
   });
 
-  it("writes the full report under --strict", () => {
-    writeSchemaLintReport(lintListResult(DIRTY_LIST), true);
+  it("writes the full report under --strict", async () => {
+    await writeSchemaLintReport(lintListResult(DIRTY_LIST), true);
     expect(stderr).toContain('Error: tool "info"');
     expect(stderr).toContain("Path: outputSchema.properties.data");
     expect(stderr).toContain("Suggestion: ");
     expect(stderr).not.toContain("Re-run with --strict");
   });
+
+  it("resolves only once stderr has taken the write", async () => {
+    // Both CLI exit paths call `process.exit()` as soon as the work returns,
+    // which discards anything still buffered on a piped stderr. The report is
+    // only safe if this settles on the write callback rather than fire-and-
+    // forget, so the fake defers its callback to a later tick.
+    let flushed = false;
+    process.stderr.write = ((
+      chunk: unknown,
+      cb?: (err?: Error | null) => void,
+    ): boolean => {
+      stderr += typeof chunk === "string" ? chunk : String(chunk);
+      setTimeout(() => {
+        flushed = true;
+        cb?.();
+      }, 0);
+      return false;
+    }) as typeof process.stderr.write;
+
+    await writeSchemaLintReport(lintListResult(DIRTY_LIST), true);
+    expect(flushed).toBe(true);
+  });
 });
 
 describe("emitResult — schema lint wiring (#1005)", () => {
@@ -109,8 +134,11 @@ describe("emitResult — schema lint wiring (#1005)", () => {
       )?.();
       return true;
     }) as typeof process.stdout.write;
-    process.stderr.write = ((chunk: unknown): boolean => {
+    process.stderr.write = ((chunk: unknown, ...rest: unknown[]): boolean => {
       stderr += typeof chunk === "string" ? chunk : String(chunk);
+      (
+        rest.find((r) => typeof r === "function") as (() => void) | undefined
+      )?.();
       return true;
     }) as typeof process.stderr.write;
   });