Delete repetition/thrash/backstop detection outright

Remove all behavior-policing repetition, cycle, and no-progress-by-turn-
count detection: the streamed-text loop detector and contentless-growth
guard on sub-agent runs (src/subagent/repetition.ts and its call sites in
run.ts), the tool-fingerprint period/cycle thrash pause and
turns-since-user-message backstop on the main director loop
(stop-policy.ts, director.ts), and the standalone period-detection
utility they both used (src/util/period-detection.ts).

These were compensating for bugs now fixed at their cause (tool-arg
rejections driving identical retries, missing prompt_cache_key,
byte-identical thinking-only turns, apply_patch reading line-numbered
output), and the streamed-text detector's own defaults were shown to
kill healthy runs reacting correctly to a stable external error.

Kept: transport-level abort handling (provider stream errors,
connection failures, retry/backoff on the model API call) and the
turn-budget / no-progress (identical tool-call fingerprint) leaf
worker limits, which are unrelated policy.

Author: TheGreatAxios

CHANGELOG.md

@@ -11,6 +11,23 @@ matching `## [X.Y.Z]` section (plus install instructions). Do not maintain
 parallel copies under `docs/` or `scripts/notes/`. At cut time: rename
 `## [Unreleased]` to `## [X.Y.Z] - YYYY-MM-DD`, then run the release script.
 
+## [Unreleased]
+
+### Agent
+
+- Removed behavior-policing repetition/cycle/thrash detection outright: the
+  streamed-text loop detector and contentless-growth guard on sub-agent runs,
+  the tool-fingerprint period/cycle thrash pause and turns-since-user-message
+  backstop on the main director loop, and the standalone period-detection
+  utility they shared. These were compensating for bugs (tool-arg rejections
+  driving identical retries, missing prompt-cache keys, byte-identical
+  thinking-only turns, line-numbered patch input) that are now fixed at their
+  cause, and the streamed-text detector's own defaults were shown to kill
+  healthy runs reacting correctly to a stable external error. Transport-level
+  abort handling (provider stream errors, connection failures, retry/backoff
+  on the model API call) and turn-budget / no-progress (identical tool-call
+  fingerprint) limits are unchanged.
+
 ## [0.2.108] - 2026-08-24
 
 ### Agent

src/agent/director.test.ts

@@ -70,11 +70,11 @@ describe("createCycleTextRecorder", () => {
   test("flush writes the buffer with a reason and resets", async () => {
     const recorder = createCycleTextRecorder(() => dir);
     recorder.handleEvent(delta("looping output"));
-    await recorder.flush("repetition");
+    await recorder.flush("cancelled");
 
     const records = await readPartialRecords();
     expect(records).toHaveLength(1);
-    expect(records[0]?.reason).toBe("repetition");
+    expect(records[0]?.reason).toBe("cancelled");
     expect(records[0]?.text).toBe("looping output");
     expect(recorder.text()).toBe("");
   });
@@ -177,7 +177,7 @@ describe("createCycleTextRecorder", () => {
     expect(recorder.text()).toBe("visible reply");
     expect(recorder.thinkingText()).toBe("0/1 1/2 2/3 ");
 
-    await recorder.flush("repetition");
+    await recorder.flush("cancelled");
     const records = await readPartialRecords();
     expect(records[0]?.text).toBe("visible reply");
     expect(records[0]?.thinkingText).toBe("0/1 1/2 2/3 ");
@@ -189,11 +189,11 @@ describe("createCycleTextRecorder", () => {
     // must still be diagnosable from thinkingText alone.
     const recorder = createCycleTextRecorder(() => dir);
     recorder.handleEvent(thinkingDelta("0/1 1/2 2/3 3/4 4/5 "));
-    const snapshot = await recorder.dispose("repetition");
+    const snapshot = await recorder.dispose("cancelled");
 
     expect(snapshot).toBe("");
     const records = await readPartialRecords();
-    expect(records[0]?.reason).toBe("repetition");
+    expect(records[0]?.reason).toBe("cancelled");
     expect(records[0]?.text).toBe("");
     expect(records[0]?.thinkingText).toBe("0/1 1/2 2/3 3/4 4/5 ");
   });

src/agent/director.ts

@@ -33,7 +33,6 @@ export function appendCycleText(
 }
 
 export type PartialFlushReason =
-  | "repetition"
   | "deadline"
   | "cancelled"
   | "interrupted"

src/session/stream-journal.test.ts

@@ -12,7 +12,6 @@ import { createDefaultDependencies } from "@intx/inference/providers";
 import { getLogger } from "@intx/log";
 import type { ConversationTurn, InferenceSource } from "@intx/types/runtime";
 import { LOG_NAMESPACE_ROOT } from "../branding.js";
-import { detectRepetition } from "../subagent/repetition.js";
 import { buildTurnSummary } from "./compactor.js";
 
 const logger = getLogger([LOG_NAMESPACE_ROOT, "session", "summarizer"]);
@@ -75,13 +74,7 @@ export function condenseTurns(turns: ConversationTurn[]): string {
         if (turn.role === "user") {
           userMessages.push(block.text.slice(0, 400));
         } else if (turn.role === "assistant" && block.text.length > 0) {
-          // Compaction often fires mid-degeneration, when the tail of the
-          // history is the model looping one phrase. Seeding the summary from
-          // those turns hands the looped text to the summarizer verbatim, so
-          // repetition-flagged turns are dropped from the excerpt entirely.
-          if (detectRepetition(block.text) === null) {
-            assistantSnippets.push(block.text.slice(0, 300));
-          }
+          assistantSnippets.push(block.text.slice(0, 300));
         }
       }
       if (block.type === "tool_call") {

src/session/stream-journal.ts

@@ -19,13 +19,11 @@ import {
   isNeverEditedSubAgentReport,
   isNoProgressSubAgentReport,
   isNoShipSubAgentReport,
-  isRepetitionSubAgentReport,
   isTurnBudgetSubAgentReport,
 } from "./stop-policy.js";
 
 /** Salvage classes that must not be re-dispatched with an identical brief. */
-export type HardBlockSalvage =
-  "no-ship" | "no-progress" | "repetition" | "never-acted" | "never-edited";
+export type HardBlockSalvage = "no-ship" | "no-progress" | "never-acted" | "never-edited";
 
 export type BriefSalvageKind =
   HardBlockSalvage | "turn-budget" | "deadline" | "stalled" | "cancelled" | "incomplete-report";
@@ -55,7 +53,6 @@ export const TURN_BUDGET_STOP_AFTER_DISPATCHES = 3;
 const HARD_BLOCK_SALVAGES = new Set<BriefSalvageKind>([
   "no-ship",
   "no-progress",
-  "repetition",
   "never-acted",
   "never-edited",
 ]);
@@ -86,7 +83,6 @@ export function isIncompleteReportSubAgentReport(report: string): boolean {
 export function classifyBriefSalvage(report: string): BriefSalvageKind | null {
   // Order: more specific salvage phrases first.
   if (isNoShipSubAgentReport(report)) return "no-ship";
-  if (isRepetitionSubAgentReport(report)) return "repetition";
   if (isNeverEditedSubAgentReport(report)) return "never-edited";
   if (isNeverActedSubAgentReport(report)) return "never-acted";
   if (isNoProgressSubAgentReport(report)) return "no-progress";

src/session/summarizer.ts

@@ -152,13 +152,13 @@ describe("forced-stop reasons", () => {
         lane({
           id: "api",
           status: "done",
-          stopReason: 'repetition — window "Groaning. " × 1363',
+          stopReason: "turn-budget — 40 turns",
         }),
         lane({ id: "docs" }),
       ],
       T0 + 1000,
     );
-    expect(updates).toEqual(['api stopped — repetition — window "Groaning. " × 1363']);
+    expect(updates).toEqual(["api stopped — turn-budget — 40 turns"]);
   });
 
   test("a cancelled lane carries its recorded reason", () => {

src/subagent/brief-dispatch.ts

@@ -19,7 +19,6 @@ import {
   formatSubAgentReport,
   nextToolCallStreak,
   parseSubAgentReport,
-  repetitionStopDetail,
   stopReasonFromReport,
   appendDeadlineParentHint,
   appendNeverActedParentHint,
@@ -196,6 +195,49 @@ describe("sub-agent stop helpers", () => {
     ).toBe("no-progress");
   });
 
+  // CL-6995: there is no repetition/similarity detector over tool results or
+  // streamed text any more. A worker that keeps getting the same failure back
+  // from the environment (e.g. a module a concurrent sibling has not finished
+  // writing) and keeps varying its own tool calls in response must run to
+  // completion rather than being killed mid-stream for "looping" on a stable
+  // external error.
+  test("many turns reacting to the same repeated tool failure still reach a normal complete", () => {
+    let consecutiveIdentical = 0;
+    let lastFingerprint: string | null = null;
+    const turns = DEFAULT_SUBAGENT_MAX_TURNS - 1;
+    for (let i = 0; i < turns; i++) {
+      // Each turn varies its own tool call (different path), even though the
+      // simulated tool result content would be identical every time.
+      const fingerprint = fingerprintToolCalls([
+        { type: "tool_call", name: "read_file", arguments: { path: `attempt-${i}.ts` } },
+      ]);
+      consecutiveIdentical = fingerprint === lastFingerprint ? consecutiveIdentical + 1 : 1;
+      lastFingerprint = fingerprint;
+      expect(
+        evaluateSubAgentStop({
+          hasToolCalls: true,
+          everHadToolCalls: true,
+          turnsCompleted: i + 1,
+          maxTurns: DEFAULT_SUBAGENT_MAX_TURNS,
+          consecutiveIdentical,
+          repeatLimit: DEFAULT_SUBAGENT_REPEAT_LIMIT,
+        }),
+      ).toBeNull();
+    }
+    // The worker finally stops calling tools and reports a real result.
+    expect(
+      evaluateSubAgentStop({
+        hasToolCalls: false,
+        everHadToolCalls: true,
+        turnsCompleted: turns + 1,
+        maxTurns: DEFAULT_SUBAGENT_MAX_TURNS,
+        consecutiveIdentical: 0,
+        repeatLimit: DEFAULT_SUBAGENT_REPEAT_LIMIT,
+        lastAssistantText: "## Summary\nDone.\n\n## Findings\nx\n\n## Blockers\nNone\n\n## Paths\n",
+      }),
+    ).toBe("complete");
+  });
+
   test("fingerprint is null when a turn has no tool calls", () => {
     expect(fingerprintToolCalls([{ type: "text" }])).toBeNull();
   });
@@ -775,20 +817,6 @@ describe("sub-agent stop helpers", () => {
   });
 
   test("forcedStopReport carries a machine-readable Stopped line the parent sees verbatim", () => {
-    const repetition = forcedStopReport(
-      "repetition",
-      "Looped window (repeated 1363x): Groaning. ",
-      'window "Groaning. " × 1363',
-    );
-    expect(repetition.startsWith('Stopped: repetition — window "Groaning. " × 1363\n')).toBe(true);
-    expect(parseSubAgentReport(repetition).stopped).toBe('repetition — window "Groaning. " × 1363');
-    expect(stopReasonFromReport(repetition)).toBe('repetition — window "Groaning. " × 1363');
-    // Survives runSubAgent's parse/format normalization round-trip.
-    const roundTripped = formatSubAgentReport(parseSubAgentReport(repetition));
-    expect(stopReasonFromReport(roundTripped)).toBe('repetition — window "Groaning. " × 1363');
-    // Classifiers and hints still fire on the unchanged Summary text.
-    expect(appendSubAgentParentHints(repetition)).toContain("degenerated into a loop");
-
     const cancelled = forcedStopReport("cancelled", "partial", "Session closed");
     expect(stopReasonFromReport(cancelled)).toBe("cancelled — Session closed");
     // Without a detail the line is the bare reason token.
@@ -808,18 +836,6 @@ describe("sub-agent stop helpers", () => {
     expect(stopReasonFromReport("## Summary\nDone.\n\n## Findings\nx")).toBe(null);
   });
 
-  test("repetitionStopDetail reports period length and repeat count, never the looped text", () => {
-    expect(repetitionStopDetail({ window: "Groaning. ", repeats: 1363 }, null)).toBe(
-      "period 10ch × 1363",
-    );
-    expect(
-      repetitionStopDetail(
-        { window: "x".repeat(500), repeats: 7 },
-        { windowMinChars: 8, repeatThreshold: 16, probeChars: 8192 },
-      ),
-    ).toBe("period 500ch × 7 (threshold 16)");
-  });
-
   test("createSubAgentRunController aborts on an explicit deadline and reports deadlineHit", async () => {
     const ctl = createSubAgentRunController(undefined, 20);
     expect(ctl.signal.aborted).toBe(false);
@@ -913,27 +929,6 @@ describe("sub-agent stop helpers", () => {
     expect(resolveSubAgentCatchOutcome({ deadlineHit: false, hadProgress: false })).toBe("rethrow");
   });
 
-  test("resolveSubAgentCatchOutcome salvages a repetition abort even with zero progress", () => {
-    expect(
-      resolveSubAgentCatchOutcome({
-        deadlineHit: false,
-        hadProgress: false,
-        repetitionHit: true,
-      }),
-    ).toBe("salvage-repetition");
-  });
-
-  test("repetition forced stop reports the loop and warns against identical re-dispatch", () => {
-    const report = forcedStopReport("repetition", "dig footer/chrome... 0/1.0 done. 1 remaining.");
-    const parsed = parseSubAgentReport(report);
-    expect(parsed.summary).toContain("degenerate repetition");
-    expect(parsed.findings).toContain("dig footer/chrome");
-    expect(parsed.blockers).toContain("will be refused");
-    expect(parsed.blockers).toContain("not maxTurns alone");
-    const hinted = appendSubAgentParentHints(report);
-    expect(hinted).toContain("Do not re-dispatch the identical brief");
-  });
-
   test("partialTextFromEvent reads stream inference.done data.turn content", () => {
     const text = partialTextFromEvent({
       type: "inference.done",
@@ -2162,8 +2157,8 @@ describe("brief re-dispatch ledger (CL-4343 / CL-5203)", () => {
     expect(ledger.admit(other).ok).toBe(true);
   });
 
-  test("hard-blocks no-progress, repetition, never-acted, never-edited; not turn-budget", () => {
-    for (const salvage of ["no-progress", "repetition", "never-acted", "never-edited"] as const) {
+  test("hard-blocks no-progress, never-acted, never-edited; not turn-budget", () => {
+    for (const salvage of ["no-progress", "never-acted", "never-edited"] as const) {
       const ledger = createBriefDispatchLedger();
       const fp = fingerprintTaskBrief({ prompt: `job ${salvage}` });
       expect(ledger.admit(fp).ok).toBe(true);
@@ -2225,7 +2220,6 @@ describe("brief re-dispatch ledger (CL-4343 / CL-5203)", () => {
 
   test("classifyBriefSalvage maps forced-stop envelopes", () => {
     expect(classifyBriefSalvage(forcedStopReport("no-progress", "x"))).toBe("no-progress");
-    expect(classifyBriefSalvage(forcedStopReport("repetition", "x"))).toBe("repetition");
     expect(classifyBriefSalvage(forcedStopReport("never-acted", "x"))).toBe("never-acted");
     expect(classifyBriefSalvage(forcedStopReport("never-edited", "x"))).toBe("never-edited");
     expect(classifyBriefSalvage(forcedStopReport("no-ship", "x"))).toBe("no-ship");

src/subagent/fleet-report.test.ts

@@ -50,7 +50,6 @@ export {
   appendDeadlineParentHint,
   appendNeverActedParentHint,
   appendNoProgressParentHint,
-  appendRepetitionParentHint,
   appendSubAgentParentHints,
   appendTurnBudgetParentHint,
   evaluateSubAgentStop,
@@ -60,7 +59,6 @@ export {
   isNeverActedSubAgentReport,
   isNeverEditedSubAgentReport,
   isNoProgressSubAgentReport,
-  isRepetitionSubAgentReport,
   isTurnBudgetSubAgentReport,
   nextToolCallStreak,
   partialTextFromEvent,
@@ -116,7 +114,6 @@ export {
   buildSubAgentPrimarySource,
   coreSubAgentWebTools,
   createSubAgentRunController,
-  repetitionStopDetail,
   runSubAgent,
   shouldRequireEvidence,
   type SubAgentRunController,