fix(devin): preserve reasoning signature association

src/adapters/devin.ts

@@ -266,8 +266,9 @@ function assistantText(message: OcxAssistantMessage): string {
  * clients of the same service write #11 thinking with #12 signature and #18
  * signature_type on the assistant prompt.
  *
- * The signature attests the thinking it was produced with, so a block without
- * one contributes its text and nothing else rather than borrowing a neighbour's.
+ * The wire has room for only one thinking/signature pair. Preserve that
+ * association by replaying the last non-empty block as a unit rather than
+ * combining independently signed blocks.
  */
 function assistantThinking(
   message: OcxAssistantMessage,
@@ -276,13 +277,11 @@ function assistantThinking(
     (part): part is Extract<typeof part, { type: "thinking" }> => part.type === "thinking",
   );
   if (blocks.length === 0) return {};
-  const thinking = blocks.map(b => b.thinking).filter(Boolean).join("\n");
-  // Only one signature can ride the prompt, so take the last block that has
-  // one: that is the block the turn actually ended on.
-  const signature = blocks.filter(b => b.signature).at(-1)?.signature;
+  const block = blocks.findLast(b => Boolean(b.thinking || b.signature));
+  if (!block) return {};
   return {
-    ...(thinking ? { thinking } : {}),
-    ...(signature ? { signature } : {}),
+    ...(block.thinking ? { thinking: block.thinking } : {}),
+    ...(block.signature ? { signature: block.signature } : {}),
   };
 }
 

structure/adapters/registry.md

@@ -42,6 +42,9 @@ Some adapters share another adapter's routed-tool semantics while retaining inde
   adapter accepts them on return. One tool's canonical identity can be another tool's advertised
   local name, and resolving that name to either owner would dispatch the call to a tool the caller
   may not have named, so it is treated as ambiguous and fails before dispatch too.
+  Assistant reasoning replay likewise follows the Cognition wire shape: because one history prompt
+  carries only one thinking/signature pair, the adapter selects the final non-empty thinking block
+  as a unit and never combines text from one block with another block's signature.
 
   There is no second Devin transport. An Agent Client Protocol adapter that spawned a local
   `devin acp` child once existed under the `devin-cli` adapter id and was removed: the CLI's

structure/data-planes/inbound-compat.md

@@ -328,3 +328,4 @@ Modern `tool` images continue through the existing following-user carrier. These
 an OpenCodex conversion limit, not a provider capability claim. Final Responses-to-adapter
 admission follows the [registry contract](../adapters/registry.md#untranslated-input-media).
 Canonical Responses identity sanitation and narrowly scoped pre-output combo recovery follow [request-local target compatibility](../runtime.md#request-local-target-compatibility); other adapter contracts remain unchanged.
+Once normalized input reaches Devin, history reasoning follows the [single-pair replay contract](../adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance).

structure/providers/chat-compat.md

@@ -338,3 +338,4 @@ prose the model reads beside them. Vendor tool execution stays disabled on both
 adapters, and Qoder's explicit refusal of original images is unchanged.
 
 Canonical Responses identity sanitation and narrowly scoped pre-output combo recovery follow [request-local target compatibility](../runtime.md#request-local-target-compatibility); other adapter contracts remain unchanged.
+Direct Devin history reasoning follows the [single-pair replay contract](../adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance), outside the translated Chat replay contract.

structure/providers/cursor.md

@@ -130,3 +130,4 @@ Translated Chat request construction uses the [inline-image budget](../transport
 
 Translated audio/file admission follows the [final-adapter input contract](../adapters/registry.md#untranslated-input-media); native raw passthrough remains separate.
 Canonical Responses identity sanitation and narrowly scoped pre-output combo recovery follow [request-local target compatibility](../runtime.md#request-local-target-compatibility); other adapter contracts remain unchanged.
+The separate Devin adapter's history reasoning follows its [single-pair replay contract](../adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance); Cursor replay is unchanged.

structure/runtime.md

@@ -412,3 +412,5 @@ Translated audio/file admission follows the [final-adapter input contract](adapt
 The combo may advance to its next eligible unattempted target before output commitment. It records no target/provider cooldown for these request-local mismatches and does not silently drop reasoning controls or raise `none` to a supported rung. Cancellation, origin/cyber-policy rejection, non-replayable post-send errors and the existing streaming commit boundary stay authoritative. Other invalid requests remain terminal.
 
 Regression coverage: `tests/responses/responses-forward-prompt-envelope.test.ts`, `tests/routing/router-combo-failover-classification.test.ts`, and `tests/server/server-combo-failover-e2e.test.ts`.
+
+Devin history reasoning preserves the [single-pair replay contract](adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance).

structure/transports/byte-accounting.md

@@ -36,3 +36,4 @@ These optimizations do not add request queues, retry policies, or RSS-based admi
 
 Translated audio/file admission follows the [final-adapter input contract](../adapters/registry.md#untranslated-input-media); native raw passthrough remains separate.
 Canonical Responses identity sanitation and narrowly scoped pre-output combo recovery follow [request-local target compatibility](../runtime.md#request-local-target-compatibility); other adapter contracts remain unchanged.
+Devin history reasoning preserves the [single-pair replay contract](../adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance); this does not change request byte accounting.

structure/transports/inventory.md

@@ -145,3 +145,4 @@ Renamed fixed-key providers receive [missing reasoning metadata](../catalog.md#r
 
 Translated audio/file admission follows the [final-adapter input contract](../adapters/registry.md#untranslated-input-media); native raw passthrough remains separate.
 Canonical Responses identity sanitation and narrowly scoped pre-output combo recovery follow [request-local target compatibility](../runtime.md#request-local-target-compatibility); other adapter contracts remain unchanged.
+The Devin transport preserves the [single-pair reasoning replay contract](../adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance) when constructing its Cognition prompt.

structure/transports/responses.md

@@ -597,4 +597,4 @@ Translated Chat request construction uses the [inline-image budget](streaming-he
 
 The [explicit model-capability contract](../config.md#explicit-per-model-capability-declarations) preserves operator declarations through provider storage and catalog capture; it does not infer upstream capability or change this surface's routing behavior.
 
-Provider-scoped approval reviewer settings are projected by the [catalog owner](../catalog.md#provider-scoped-approval-reviewer); this surface retains its existing routing, transport and account-selection behavior. Translated audio/file admission follows the [final-adapter input contract](../adapters/registry.md#untranslated-input-media); native raw passthrough remains separate.
+Provider-scoped approval reviewer settings are projected by the [catalog owner](../catalog.md#provider-scoped-approval-reviewer); this surface retains its existing routing, transport and account-selection behavior. Translated audio/file admission follows the [final-adapter input contract](../adapters/registry.md#untranslated-input-media); native raw passthrough remains separate. Devin history reasoning preserves the [single-pair replay contract](../adapters/registry.md#semantic-inheritance-is-not-constructor-inheritance) after Responses parsing keeps independently signed blocks separate.

tests/providers/devin-hardening.test.ts

@@ -496,6 +496,32 @@ describe("devin reasoning replay", () => {
     expect(history.find(m => m.role === "assistant")?.thinking).toBe("only thought");
   });
 
+  test("multiple thinking blocks keep the final block's text and signature together", () => {
+    const history = mapOcxMessagesToDevin(parsedWith([
+      {
+        role: "assistant",
+        content: [
+          { type: "thinking", thinking: "first thought", signature: "sig-first" },
+          { type: "thinking", thinking: "final thought", signature: "sig-final" },
+        ],
+      },
+    ]));
+    expect(history[0]?.thinking).toBe("final thought");
+    expect(history[0]?.signature).toBe("sig-final");
+
+    const unsignedLast = mapOcxMessagesToDevin(parsedWith([
+      {
+        role: "assistant",
+        content: [
+          { type: "thinking", thinking: "signed thought", signature: "sig-signed" },
+          { type: "thinking", thinking: "unsigned thought" },
+        ],
+      },
+    ]));
+    expect(unsignedLast[0]?.thinking).toBe("unsigned thought");
+    expect(unsignedLast[0]?.signature).toBeUndefined();
+  });
+
   test("the encoded prompt carries thinking at #11 and its signature at #12", () => {
     const req = buildGetChatMessageRequestForTests({
       apiKey: "devin-session-token$x",