🤖 fix: preserve openai reasoning replay ids (#17792)

What:
- disable tool-call id sanitization for OpenAI/OpenAI Codex transcript policy
- gate id sanitization in image sanitizer to full mode only
- keep orphan reasoning downgrade scoped to OpenAI model-switch replay path
- update transcript policy, session-history, sanitizer, and reasoning replay tests
- document OpenAI model-switch orphan-reasoning cleanup behavior in transcript hygiene reference

Why:
- OpenAI Responses replay depends on canonical call_id|fc_id pairings for reasoning followers
- strict id rewriting in OpenAI path breaks follower matching and triggers rs_* orphan 400s
- limiting scope avoids behavior expansion while fixing the identified regression

Tests:
- pnpm vitest run src/agents/transcript-policy.test.ts src/agents/pi-embedded-runner.sanitize-session-history.test.ts src/agents/openai-responses.reasoning-replay.test.ts
- pnpm vitest run --config vitest.e2e.config.ts src/agents/transcript-policy.e2e.test.ts src/agents/pi-embedded-runner.sanitize-session-history.e2e.test.ts src/agents/pi-embedded-helpers.sanitize-session-messages-images.removes-empty-assistant-text-blocks-but-preserves.e2e.test.ts src/agents/pi-embedded-helpers.sanitizeuserfacingtext.e2e.test.ts
- pnpm lint
- pnpm format:check
- pnpm check:docs
- pnpm test (fails in current macOS bash 3.2 env at test/git-hooks-pre-commit.integration.test.ts: mapfile not found)

src/agents/pi-embedded-helpers.sanitizeuserfacingtext.e2e.test.ts

@@ -294,6 +294,27 @@ describe("downgradeOpenAIReasoningBlocks", () => {
     // oxlint-disable-next-line typescript/no-explicit-any
     expect(downgradeOpenAIReasoningBlocks(input as any)).toEqual(input);
   });
+
+  it("is idempotent for orphaned reasoning cleanup", () => {
+    const input = [
+      {
+        role: "assistant",
+        content: [
+          {
+            type: "thinking",
+            thinkingSignature: JSON.stringify({ id: "rs_orphan", type: "reasoning" }),
+          },
+        ],
+      },
+      { role: "user", content: "next" },
+    ];
+
+    // oxlint-disable-next-line typescript/no-explicit-any
+    const once = downgradeOpenAIReasoningBlocks(input as any);
+    // oxlint-disable-next-line typescript/no-explicit-any
+    const twice = downgradeOpenAIReasoningBlocks(once as any);
+    expect(twice).toEqual(once);
+  });
 });
 
 describe("normalizeTextForComparison", () => {