diff --git a/src/application/reverse/ReverseEngineeringService.ts b/src/application/reverse/ReverseEngineeringService.ts
index 23a9613f77..68d5cb6c02 100644
--- a/src/application/reverse/ReverseEngineeringService.ts
+++ b/src/application/reverse/ReverseEngineeringService.ts
@@ -1057,7 +1057,11 @@ export const digestFile = async (
       remainingMs,
     );
     const abort = (): void => {
-      stream.destroy(new AnalysisCancelledError("artifact_digest"));
+      stream.destroy(
+        new AnalysisCancelledError("artifact_digest", {
+          cause: signal?.reason,
+        }),
+      );
     };
     const cleanup = (): void => {
       clearTimeout(timer);
@@ -1066,7 +1070,11 @@ export const digestFile = async (
     if (signal?.aborted) {
       cleanup();
       stream.destroy();
-      rejectDigest(new AnalysisCancelledError("artifact_digest"));
+      rejectDigest(
+        new AnalysisCancelledError("artifact_digest", {
+          cause: signal.reason,
+        }),
+      );
       return;
     }
     signal?.addEventListener("abort", abort, { once: true });
@@ -1139,7 +1147,9 @@ const statWithDeadline = (
   timeoutMs: number,
 ): Promise<Stats> => {
   if (signal?.aborted)
-    return Promise.reject(new AnalysisCancelledError("artifact_digest"));
+    return Promise.reject(
+      new AnalysisCancelledError("artifact_digest", { cause: signal.reason }),
+    );
   return new Promise<Stats>((resolveStat, rejectStat) => {
     let settled = false;
     const finish = (outcome: Result<Stats, unknown>): void => {
@@ -1151,7 +1161,13 @@ const statWithDeadline = (
       else rejectStat(outcome.error);
     };
     const abort = (): void =>
-      finish(err(new AnalysisCancelledError("artifact_digest")));
+      finish(
+        err(
+          new AnalysisCancelledError("artifact_digest", {
+            cause: signal?.reason,
+          }),
+        ),
+      );
     const timer = setTimeout(
       () =>
         finish(
diff --git a/src/cli/environmentCommands.ts b/src/cli/environmentCommands.ts
index 6445523de5..abce912196 100644
--- a/src/cli/environmentCommands.ts
+++ b/src/cli/environmentCommands.ts
@@ -124,8 +124,12 @@ interface ServeInputs {
   readonly served: ServedState;
 }
 
-const cancelledServe = (): JsonValue =>
-  cliError(new AnalysisCancelledError(CLI_COMMANDS.environmentServe));
+const cancelledServe = (signal: AbortSignal): JsonValue =>
+  cliError(
+    new AnalysisCancelledError(CLI_COMMANDS.environmentServe, {
+      cause: signal.reason,
+    }),
+  );
 
 /** Pure replay, as `--replay-only` asks for: no state is derived. */
 const REPLAY_ONLY: ServedState = {
@@ -149,14 +153,14 @@ const loadServeInputs = async (
   if (!evidence.ok) return evidence;
   const { loadEnvironmentSource } =
     await import("../application/environment/environmentSource.js");
-  if (signal.aborted) return err(cancelledServe());
+  if (signal.aborted) return err(cancelledServe(signal));
   const source = loadEnvironmentSource(manifest.value, evidence.value);
   if (!source.ok) return err(cliError(source.error));
   if (input.replayOnly)
     return ok({ source: source.value, served: REPLAY_ONLY });
   const { prepareServedState } =
     await import("../application/environment/environmentState.js");
-  if (signal.aborted) return err(cancelledServe());
+  if (signal.aborted) return err(cancelledServe(signal));
   return ok({
     source: source.value,
     served: prepareServedState(source.value, evidence.value, {
@@ -172,7 +176,7 @@ const serveEnvironmentCommand = async (
   logger: Logger,
   signal: AbortSignal,
 ): Promise<JsonValue> => {
-  if (signal.aborted) return cancelledServe();
+  if (signal.aborted) return cancelledServe(signal);
   const endpoint = parseMcpHttpEndpoint(environment, {
     ...(input.host === undefined ? {} : { host: input.host }),
     ...(input.port === undefined ? {} : { port: input.port }),
@@ -192,13 +196,13 @@ const serveEnvironmentCommand = async (
       { code: report.code, error: report.message },
       "Environment state unavailable; serving recorded replay",
     );
-  if (signal.aborted) return cancelledServe();
+  if (signal.aborted) return cancelledServe(signal);
   // Loaded here so registering the command catalog never loads the HTTP listener.
   const { serveEnvironment } =
     await import("../server/environment/serveEnvironment.js");
   const { StreamableHttpListenError } =
     await import("../server/http/streamableHttpListenError.js");
-  if (signal.aborted) return cancelledServe();
+  if (signal.aborted) return cancelledServe(signal);
   // A listener that fails after binding ends the command instead of serving nothing.
   let failListener: (error: StreamableHttpListenError) => void = () =>
     undefined;
@@ -221,7 +225,8 @@ const serveEnvironmentCommand = async (
     if (!started.ok) return cliError(started.error);
     served = started.value;
   } catch (cause: unknown) {
-    if (signal.aborted && cause === signal.reason) return cancelledServe();
+    if (signal.aborted && cause === signal.reason)
+      return cancelledServe(signal);
     if (!(cause instanceof StreamableHttpListenError)) throw cause;
     return cliError(transportError(endpoint.value, cause));
   }
@@ -449,7 +454,11 @@ const buildEnvironmentCommand = async (
     capture = read.value;
   }
   if (signal.aborted)
-    return cliError(new AnalysisCancelledError(CLI_COMMANDS.environmentBuild));
+    return cliError(
+      new AnalysisCancelledError(CLI_COMMANDS.environmentBuild, {
+        cause: signal.reason,
+      }),
+    );
   const captureInput: EnvironmentBuildCaptureInput = kind.value;
   const built = await buildEnvironment({
     capture,
diff --git a/src/gdb/GdbSessionManager.ts b/src/gdb/GdbSessionManager.ts
index fc7d71f1e4..9f5e72143e 100644
--- a/src/gdb/GdbSessionManager.ts
+++ b/src/gdb/GdbSessionManager.ts
@@ -696,7 +696,11 @@ export class GdbSessionManager {
     >
   > {
     if (signal?.aborted)
-      return err(new AnalysisCancelledError("start_gdb_session"));
+      return err(
+        new AnalysisCancelledError("start_gdb_session", {
+          cause: signal.reason,
+        }),
+      );
     const occupied = this.#sessions.size + this.#sessionReservations;
     if (occupied >= this.#maxSessions)
       return err(
@@ -896,7 +900,11 @@ export class GdbSessionManager {
         session.startupResolve = resolve;
         session.startupReject = reject;
         startupAbortListener = () =>
-          reject(new AnalysisCancelledError("start_gdb_session"));
+          reject(
+            new AnalysisCancelledError("start_gdb_session", {
+              cause: signal?.reason,
+            }),
+          );
         signal?.addEventListener("abort", startupAbortListener, {
           once: true,
         });
@@ -923,7 +931,9 @@ export class GdbSessionManager {
         startupTimer.unref();
       });
       if (signal?.aborted)
-        throw new AnalysisCancelledError("start_gdb_session");
+        throw new AnalysisCancelledError("start_gdb_session", {
+          cause: signal.reason,
+        });
       const autoLoad = await this.#request(
         session,
         "-gdb-set auto-load off",
@@ -977,11 +987,15 @@ export class GdbSessionManager {
         session.inferiorTtyVerified = true;
       }
       if (signal?.aborted)
-        throw new AnalysisCancelledError("start_gdb_session");
+        throw new AnalysisCancelledError("start_gdb_session", {
+          cause: signal.reason,
+        });
       // Give queued exit notifications a turn before publishing startup.
       await new Promise<void>((resolve) => setImmediate(resolve));
       if (signal?.aborted)
-        throw new AnalysisCancelledError("start_gdb_session");
+        throw new AnalysisCancelledError("start_gdb_session", {
+          cause: signal.reason,
+        });
       if (session.exited || session.protocolError !== undefined)
         throw new Error(
           session.protocolError ?? "GDB exited during startup readiness.",
diff --git a/tests/boundary/providers/GdbSessionManagerCoverage.test.ts b/tests/boundary/providers/GdbSessionManagerCoverage.test.ts
index 01f4c973aa..b10f21b6d0 100644
--- a/tests/boundary/providers/GdbSessionManagerCoverage.test.ts
+++ b/tests/boundary/providers/GdbSessionManagerCoverage.test.ts
@@ -1970,19 +1970,23 @@ it("handles a start signal that becomes aborted during listener registration", a
 
 it("handles cancellation after the automatic-loading response", async () => {
   const controller = new AbortController();
+  const reason = { source: "caller after automatic loading" };
   const fake = createFakeSpawner((child, token, command) => {
     child.stdout.write(
       command.includes("list-thread-groups")
         ? `${token}^done,groups=[]\n`
         : `${token}^done\n`,
     );
-    if (command.includes("auto-load off")) controller.abort();
+    if (command.includes("auto-load off")) controller.abort(reason);
   });
   const manager = managerWithFakeSpawner(fake.spawnProcess);
   const started = await manager.start(controller.signal);
 
   expect(started.ok).toBe(false);
-  if (!started.ok) expect(started.error._tag).toBe("AnalysisCancelledError");
+  if (!started.ok) {
+    expect(started.error._tag).toBe("AnalysisCancelledError");
+    expect(started.error.cause).toBe(reason);
+  }
 });
 
 it("reports an MI stream failure when the child has no stdin pipe", async () => {
diff --git a/tests/composition/reverseEngineering.test.ts b/tests/composition/reverseEngineering.test.ts
index 7be3eac0d8..a1cf245597 100644
--- a/tests/composition/reverseEngineering.test.ts
+++ b/tests/composition/reverseEngineering.test.ts
@@ -12,6 +12,7 @@ import { TestReverseEngineeringService as ReverseEngineeringService } from "../s
 import { providerSnapshot } from "../support/reverseEngineeringCompositionFixtures.js";
 import { createReverseEngineeringService } from "../../src/composition/reverseEngineering.js";
 import { projectAnalysisError } from "../../src/domain/analysisErrorProjection.js";
+import { AnalysisCancelledError } from "../../src/domain/analysisErrorCore.js";
 import { REVERSE_ENGINEERING_TOOL_CONTRACTS } from "../../src/contracts/reverseEngineeringToolContracts.js";
 
 describe("reverse engineering command services", () => {
@@ -574,6 +575,41 @@ it("shares one preflight deadline across stat and digest", async () => {
   expect(performance.now() - started).toBeLessThan(280);
 });
 
+it("retains an explicit null reason when digest admission is already cancelled", async () => {
+  const controller = new AbortController();
+  controller.abort(null);
+  await expect(
+    digestFile("/tmp/rea-cancelled-digest", controller.signal),
+  ).rejects.toMatchObject({
+    _tag: "AnalysisCancelledError",
+    cause: null,
+  });
+});
+
+it("retains an object reason when cancellation interrupts an active digest stream", async () => {
+  const controller = new AbortController();
+  const reason = { source: "caller digest cancellation" };
+  const stat = async (): Promise<Stats> => ({ isFile: () => true }) as Stats;
+  const open = () => {
+    const stream = new PassThrough();
+    queueMicrotask(() => controller.abort(reason));
+    return stream as unknown as ReturnType<
+      typeof import("node:fs").createReadStream
+    >;
+  };
+  const failure: unknown = await digestFile(
+    "/tmp/rea-cancelled-stream",
+    controller.signal,
+    stat,
+    1_000,
+    open,
+  ).catch((cause: unknown) => cause);
+  expect(failure).toBeInstanceOf(AnalysisCancelledError);
+  if (!(failure instanceof AnalysisCancelledError))
+    throw new Error("Expected digest cancellation");
+  expect(failure.cause).toBe(reason);
+});
+
 it("forwards selected and omitted deadlines through the production command runner", async () => {
   const directory = await mkdtemp(join(tmpdir(), "rea-owned-timeout-"));
   const path = join(directory, "fixture.bin");