Fix default failure-cause misclassification as prompt_exhaustion

buildEmptyOutputOutcome() fell back to "prompt_exhaustion" whenever no PROMPT_EXHAUSTION_ERROR_CATEGORIES, REQUEST_REJECTION_ERROR_CATEGORIES, or 5xx engine-outage evidence was found. Absence of evidence is not evidence of token/invocation-limit exhaustion, so most missing_terminal_safe_output incompletions (no matched category, 0 retries observed) were mislabeled as prompt_exhaustion. This inflated the prompt_exhaustion failure-issue cluster (#66817) across unrelated workflows such as Avenger. Classify the unmatched case as a new "unknown" failure cause instead of defaulting to prompt_exhaustion, with a matching issue-title mapping. Fixes #66817 Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
pelikhan · Oct 10, 2026 · Oct 10, 2026 · Oct 10, 2026 · Oct 10, 2026 · Oct 10, 2026
commit 30b79f66db3687a2cf4838db3e113f4f7586fbfe
diff --git a/actions/setup/js/collect_ndjson_output.test.cjs b/actions/setup/js/collect_ndjson_output.test.cjs
@@ -10,14 +10,14 @@ const incompleteOutput = JSON.stringify({
     {
       type: "report_incomplete",
       reason: "missing_terminal_safe_output",
-      failureCause: "prompt_exhaustion",
+      failureCause: "unknown",
       retryCount: 0,
-      details: "Agent finished without emitting a terminal safe output; task completion could not be confirmed.\nFailure classification: prompt_exhaustion\nRetry attempts observed: 0",
+      details: "Agent finished without emitting a terminal safe output; task completion could not be confirmed.\nFailure classification: unknown\nRetry attempts observed: 0",
     },
   ],
   errors: [],
   collectorEmptyOutputCause: "missing_terminal_safe_output",
-  collectorFailureCause: "prompt_exhaustion",
+  collectorFailureCause: "unknown",
   collectorRetryCount: 0,
 });
 describe("collect_ndjson_output.cjs", () => {

diff --git a/actions/setup/js/empty_output_outcome.cjs b/actions/setup/js/empty_output_outcome.cjs
@@ -21,6 +21,7 @@ const EMPTY_OUTPUT_FAILURE_CAUSES = Object.freeze({
   engine_outage: "experienced an engine outage",
   request_rejection: "had a request rejected",
   prompt_exhaustion: "exhausted its prompt",
+  unknown: "finished without a clear failure cause",
 });
 
 const PROMPT_EXHAUSTION_ERROR_CATEGORIES = new Set(["effective_tokens_limit_exceeded", "invocation_cap_exceeded"]);
@@ -166,7 +167,9 @@ function buildEmptyOutputOutcome(errors, rootDir = "/tmp/gh-aw") {
   const isPromptExhaustion = executionCategories.some(category => PROMPT_EXHAUSTION_ERROR_CATEGORIES.has(category));
   const isRequestRejection = ["invalid_safe_outputs", "safeoutputs_cli_error"].includes(reason) || executionCategories.some(category => REQUEST_REJECTION_ERROR_CATEGORIES.has(category)) || errorCodes.some(code => code >= 400 && code < 500);
   const isEngineOutage = reason === "engine_driver_failure" || executionCategories.some(category => ["agentic_engine_timeout", "capi_server_error", "sandbox_runtime_crash"].includes(category)) || errorCodes.some(code => code >= 500);
-  const failureCause = isPromptExhaustion ? "prompt_exhaustion" : isRequestRejection ? "request_rejection" : isEngineOutage ? "engine_outage" : "prompt_exhaustion";
+  // Absence of evidence is not evidence of prompt exhaustion: without a matched category
+  // or status code, classify as "unknown" instead of guessing prompt_exhaustion.
+  const failureCause = isPromptExhaustion ? "prompt_exhaustion" : isRequestRejection ? "request_rejection" : isEngineOutage ? "engine_outage" : "unknown";
   const retryEvents = events.filter(event => event.type === "claude.api_retry" || (event.type === "system" && event.data.subtype === "api_retry"));
   const harnessRetryLines = stdio.split(/\r?\n/).filter(line => /^\[(?:copilot|claude|codex)-harness\].*\bretrying\b/i.test(line));
   const harnessRetryCount = harnessRetryLines.length;

diff --git a/actions/setup/js/empty_output_outcome.test.cjs b/actions/setup/js/empty_output_outcome.test.cjs
@@ -27,9 +27,9 @@ describe("empty output outcome", () => {
     expect(buildEmptyOutputOutcome([], rootDir)).toEqual({
       type: "report_incomplete",
       reason: "missing_terminal_safe_output",
-      failureCause: "prompt_exhaustion",
+      failureCause: "unknown",
       retryCount: 0,
-      details: "Agent finished without emitting a terminal safe output; task completion could not be confirmed.\nFailure classification: prompt_exhaustion\nRetry attempts observed: 0",
+      details: "Agent finished without emitting a terminal safe output; task completion could not be confirmed.\nFailure classification: unknown\nRetry attempts observed: 0",
     });
   });
 

diff --git a/actions/setup/js/handle_agent_failure.test.cjs b/actions/setup/js/handle_agent_failure.test.cjs
@@ -538,6 +538,7 @@ describe("handle_agent_failure", () => {
       ["engine_outage", "[aw] Test Workflow experienced an engine outage"],
       ["request_rejection", "[aw] Test Workflow had a request rejected"],
       ["prompt_exhaustion", "[aw] Test Workflow exhausted its prompt"],
+      ["unknown", "[aw] Test Workflow finished without a clear failure cause"],
     ])("uses the classified terminal-output cause %s in the issue title", (terminalOutputFailureCause, title) => {
       expect(buildFailureIssueTitle({ ...baseOptions, terminalOutputFailureCause })).toBe(title);
     });