diff --git a/src/resources/extensions/gsd/forensics.ts b/src/resources/extensions/gsd/forensics.ts
index 81cc69da2..ba2746f8b 100644
--- a/src/resources/extensions/gsd/forensics.ts
+++ b/src/resources/extensions/gsd/forensics.ts
@@ -38,7 +38,7 @@ import { ensurePreferencesFile, serializePreferencesToFrontmatter } from "./comm
 
 // ─── Types ────────────────────────────────────────────────────────────────────
 
-interface ForensicAnomaly {
+export interface ForensicAnomaly {
   type: "stuck-loop" | "cost-spike" | "timeout" | "missing-artifact" | "crash" | "doctor-issue" | "error-trace" | "journal-stuck" | "journal-guard-block" | "journal-rapid-iterations" | "journal-worktree-failure";
   severity: "info" | "warning" | "error";
   unitType?: string;
@@ -640,13 +640,29 @@ function getDbCompletionCounts(): DbCompletionCounts | null {
 
 // ─── Anomaly Detectors ───────────────────────────────────────────────────────
 
-function detectStuckLoops(units: UnitMetrics[], anomalies: ForensicAnomaly[]): void {
-  const counts = new Map<string, number>();
+/**
+ * Detect units that were dispatched multiple times (stuck in a loop).
+ *
+ * Counts distinct dispatches by grouping on (type, id, startedAt) first to
+ * collapse idle-watchdog duplicate snapshots (#1943), then counts unique
+ * startedAt values per type/id to determine actual dispatch count.
+ *
+ * Exported for testability.
+ */
+export function detectStuckLoops(units: UnitMetrics[], anomalies: ForensicAnomaly[]): void {
+  // First, collect unique startedAt values per type/id key
+  const dispatchMap = new Map<string, Set<number>>();
   for (const u of units) {
     const key = `${u.type}/${u.id}`;
-    counts.set(key, (counts.get(key) ?? 0) + 1);
+    let starts = dispatchMap.get(key);
+    if (!starts) {
+      starts = new Set();
+      dispatchMap.set(key, starts);
+    }
+    starts.add(u.startedAt);
   }
-  for (const [key, count] of counts) {
+  for (const [key, starts] of dispatchMap) {
+    const count = starts.size;
     if (count > 1) {
       const [unitType, ...idParts] = key.split("/");
       anomalies.push({
diff --git a/src/resources/extensions/gsd/metrics.ts b/src/resources/extensions/gsd/metrics.ts
index 1467499e4..a29d4f39d 100644
--- a/src/resources/extensions/gsd/metrics.ts
+++ b/src/resources/extensions/gsd/metrics.ts
@@ -567,7 +567,34 @@ export function loadLedgerFromDisk(base: string): MetricsLedger | null {
 }
 
 function loadLedger(base: string): MetricsLedger {
-  return loadJsonFile(metricsPath(base), isMetricsLedger, defaultLedger);
+  const raw = loadJsonFile(metricsPath(base), isMetricsLedger, defaultLedger);
+  const before = raw.units.length;
+  raw.units = deduplicateUnits(raw.units);
+  if (raw.units.length < before) {
+    // Persist the cleaned ledger so duplicates don't re-accumulate
+    saveLedger(base, raw);
+  }
+  return raw;
+}
+
+/**
+ * Collapse duplicate entries with the same (type, id, startedAt) triple.
+ * Keeps the entry with the highest finishedAt (the most complete snapshot).
+ *
+ * This is a defensive measure against idle-watchdog race conditions that can
+ * produce duplicate entries on disk despite the in-memory idempotency guard
+ * in snapshotUnitMetrics(). See #1943.
+ */
+function deduplicateUnits(units: UnitMetrics[]): UnitMetrics[] {
+  const map = new Map<string, UnitMetrics>();
+  for (const u of units) {
+    const key = `${u.type}\0${u.id}\0${u.startedAt}`;
+    const existing = map.get(key);
+    if (!existing || u.finishedAt > existing.finishedAt) {
+      map.set(key, u);
+    }
+  }
+  return Array.from(map.values());
 }
 
 function saveLedger(base: string, data: MetricsLedger): void {
diff --git a/src/resources/extensions/gsd/tests/forensics-stuck-loops.test.ts b/src/resources/extensions/gsd/tests/forensics-stuck-loops.test.ts
new file mode 100644
index 000000000..555570bab
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/forensics-stuck-loops.test.ts
@@ -0,0 +1,103 @@
+/**
+ * Forensics detectStuckLoops tests — #1943
+ *
+ * Verifies that detectStuckLoops counts distinct dispatches (unique startedAt
+ * values per type/id) instead of raw entry count, which produces false-positive
+ * stuck-loop anomalies when idle-watchdog duplicate metrics entries exist.
+ */
+
+import test from "node:test";
+import assert from "node:assert/strict";
+import type { UnitMetrics } from "../metrics.js";
+import { detectStuckLoops, type ForensicAnomaly } from "../forensics.js";
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+function makeUnit(overrides: Partial<UnitMetrics> = {}): UnitMetrics {
+  return {
+    type: "execute-task",
+    id: "M001/S01/T01",
+    model: "claude-sonnet-4-20250514",
+    startedAt: 1000,
+    finishedAt: 2000,
+    tokens: { input: 1000, output: 500, cacheRead: 200, cacheWrite: 100, total: 1800 },
+    cost: 0.05,
+    toolCalls: 3,
+    assistantMessages: 2,
+    userMessages: 1,
+    ...overrides,
+  };
+}
+
+
+// ── Tests ────────────────────────────────────────────────────────────────────
+
+test("#1943 detectStuckLoops does not flag idle-watchdog duplicates as stuck loops", () => {
+  const anomalies: ForensicAnomaly[] = [];
+  const startedAt = 1774011016218;
+
+  // 20 entries with the SAME startedAt — these are idle-watchdog duplicates,
+  // not real re-dispatches. They should count as 1 dispatch.
+  const units: UnitMetrics[] = [];
+  for (let i = 0; i < 20; i++) {
+    units.push(makeUnit({
+      type: "research-slice",
+      id: "M009/S02",
+      startedAt,
+      finishedAt: startedAt + (i + 1) * 15000,
+      cost: 1.50 + i * 0.05,
+      toolCalls: 0,
+    }));
+  }
+
+  detectStuckLoops(units, anomalies);
+
+  // A single dispatch (same startedAt) should NOT trigger a stuck-loop anomaly
+  assert.equal(
+    anomalies.length, 0,
+    `expected 0 anomalies for 20 watchdog snapshots of the same dispatch, got ${anomalies.length}: ${anomalies.map(a => a.summary).join(", ")}`,
+  );
+});
+
+test("#1943 detectStuckLoops correctly flags real re-dispatches", () => {
+  const anomalies: ForensicAnomaly[] = [];
+
+  // 3 entries with DIFFERENT startedAt values — these are real re-dispatches
+  const units: UnitMetrics[] = [
+    makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 1000, finishedAt: 2000, cost: 0.05 }),
+    makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 3000, finishedAt: 4000, cost: 0.06 }),
+    makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 5000, finishedAt: 6000, cost: 0.07 }),
+  ];
+
+  detectStuckLoops(units, anomalies);
+
+  assert.equal(anomalies.length, 1, "3 distinct dispatches of the same unit should flag 1 anomaly");
+  assert.equal(anomalies[0].type, "stuck-loop");
+  assert.ok(anomalies[0].summary.includes("3 times"), `summary should mention 3 dispatches: ${anomalies[0].summary}`);
+});
+
+test("#1943 detectStuckLoops ignores watchdog duplicates but flags real re-dispatches in mixed data", () => {
+  const anomalies: ForensicAnomaly[] = [];
+
+  const units: UnitMetrics[] = [
+    // 5 watchdog duplicates for dispatch 1 (same startedAt = 1000)
+    ...Array.from({ length: 5 }, (_, i) =>
+      makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 1000, finishedAt: 1000 + (i + 1) * 15000, cost: 0.05 + i * 0.01 }),
+    ),
+    // 3 watchdog duplicates for dispatch 2 (same startedAt = 100000)
+    ...Array.from({ length: 3 }, (_, i) =>
+      makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 100000, finishedAt: 100000 + (i + 1) * 15000, cost: 0.08 + i * 0.01 }),
+    ),
+    // 1 entry for dispatch 3 (startedAt = 200000)
+    makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 200000, finishedAt: 260000, cost: 0.10 }),
+    // Different unit — only 1 dispatch, should NOT be flagged
+    makeUnit({ type: "plan-slice", id: "M001/S01", startedAt: 500, finishedAt: 1500, cost: 0.02 }),
+  ];
+
+  detectStuckLoops(units, anomalies);
+
+  // M001/S01/T01 has 3 distinct dispatches (startedAt: 1000, 100000, 200000) — should be flagged
+  // M001/S01 has 1 dispatch — should NOT be flagged
+  assert.equal(anomalies.length, 1, `expected 1 anomaly (for the 3x dispatched task), got ${anomalies.length}`);
+  assert.ok(anomalies[0].summary.includes("3 times"));
+});
diff --git a/src/resources/extensions/gsd/tests/metrics.test.ts b/src/resources/extensions/gsd/tests/metrics.test.ts
index 98782460e..dc221531a 100644
--- a/src/resources/extensions/gsd/tests/metrics.test.ts
+++ b/src/resources/extensions/gsd/tests/metrics.test.ts
@@ -6,7 +6,7 @@
 
 import test from "node:test";
 import assert from "node:assert/strict";
-import { mkdtempSync, mkdirSync, readFileSync, rmSync } from "node:fs";
+import { mkdtempSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import { tmpdir } from "node:os";
 import {
@@ -382,3 +382,118 @@ test("snapshotUnitMetrics counts toolCall blocks correctly (#1713)", () => {
     rmSync(tmpBase, { recursive: true, force: true });
   }
 });
+
+// ── #1943 — Duplicate metrics entries from idle watchdog ──────────────────────
+
+test("#1943 initMetrics deduplicates entries loaded from a corrupted disk ledger", () => {
+  const tmpBase = mkdtempSync(join(tmpdir(), "gsd-metrics-dedup-load-"));
+  mkdirSync(join(tmpBase, ".gsd"), { recursive: true });
+
+  try {
+    resetMetrics();
+
+    // Simulate a corrupted metrics.json with duplicate entries on disk
+    // (same type+id+startedAt but different finishedAt — idle watchdog pattern)
+    const corruptedLedger: MetricsLedger = {
+      version: 1,
+      projectStartedAt: 1700000000000,
+      units: [
+        makeUnit({ type: "research-slice", id: "M009/S02", startedAt: 1774011016218, finishedAt: 1774011031218, cost: 1.50, tokens: { input: 6600000, output: 100000, cacheRead: 0, cacheWrite: 0, total: 6700000 } }),
+        makeUnit({ type: "research-slice", id: "M009/S02", startedAt: 1774011016218, finishedAt: 1774011046218, cost: 1.55, tokens: { input: 6800000, output: 110000, cacheRead: 0, cacheWrite: 0, total: 6910000 } }),
+        makeUnit({ type: "research-slice", id: "M009/S02", startedAt: 1774011016218, finishedAt: 1774011061218, cost: 1.60, tokens: { input: 7000000, output: 120000, cacheRead: 0, cacheWrite: 0, total: 7120000 } }),
+        makeUnit({ type: "research-slice", id: "M009/S02", startedAt: 1774011016218, finishedAt: 1774011076218, cost: 1.65, tokens: { input: 7200000, output: 130000, cacheRead: 0, cacheWrite: 0, total: 7330000 } }),
+        // A different unit — should be preserved
+        makeUnit({ type: "execute-task", id: "M001/S01/T01", startedAt: 1774012000000, finishedAt: 1774012060000, cost: 0.50 }),
+      ],
+    };
+    writeFileSync(
+      join(tmpBase, ".gsd", "metrics.json"),
+      JSON.stringify(corruptedLedger, null, 2),
+    );
+
+    // Load the corrupted ledger — duplicates should be collapsed on load
+    initMetrics(tmpBase);
+    const ledger = getLedger();
+    assert.ok(ledger);
+
+    // The 4 entries with identical (type, id, startedAt) should collapse to 1,
+    // keeping the latest (highest finishedAt). Plus the 1 different unit = 2 total.
+    assert.equal(
+      ledger!.units.length, 2,
+      `expected 2 entries after dedup (1 collapsed group + 1 unique), got ${ledger!.units.length}`,
+    );
+
+    // The surviving duplicate should be the one with the latest finishedAt
+    const researchEntry = ledger!.units.find(u => u.type === "research-slice");
+    assert.ok(researchEntry);
+    assert.equal(researchEntry!.finishedAt, 1774011076218, "should keep the latest finishedAt");
+    assert.equal(researchEntry!.cost, 1.65, "should keep the latest cost");
+
+    // The on-disk file should also be deduplicated
+    const diskRaw = readFileSync(join(tmpBase, ".gsd", "metrics.json"), "utf-8");
+    const diskLedger: MetricsLedger = JSON.parse(diskRaw);
+    assert.equal(diskLedger.units.length, 2, "disk should also have deduplicated entries");
+  } finally {
+    resetMetrics();
+    rmSync(tmpBase, { recursive: true, force: true });
+  }
+});
+
+test("#1943 getProjectTotals reports correct cost after dedup (no 35% inflation)", () => {
+  // Simulate the exact scenario from the issue: 20 entries for a single dispatch
+  // with monotonically increasing token counts and 15s-apart finishedAt values
+  const startedAt = 1774011016218;
+  const baseCost = 1.50;
+  const duplicateUnits: UnitMetrics[] = [];
+
+  for (let i = 0; i < 20; i++) {
+    duplicateUnits.push(makeUnit({
+      type: "research-slice",
+      id: "M009/S02",
+      startedAt,
+      finishedAt: startedAt + (i + 1) * 15000,
+      cost: baseCost + i * 0.05,
+      toolCalls: 0,
+      tokens: {
+        input: 6600000 + i * 200000,
+        output: 100000 + i * 10000,
+        cacheRead: 0,
+        cacheWrite: 0,
+        total: 6700000 + i * 210000,
+      },
+    }));
+  }
+
+  // Without dedup, getProjectTotals would sum all 20 entries' costs
+  const rawTotals = getProjectTotals(duplicateUnits);
+  // With dedup (only last entry should count), cost should be the last entry's cost
+  const lastEntryCost = duplicateUnits[duplicateUnits.length - 1].cost;
+
+  // This test documents the bug: raw totals inflate cost by summing duplicates
+  assert.ok(
+    rawTotals.cost > lastEntryCost * 2,
+    "raw totals with duplicates inflate cost (bug demonstration)",
+  );
+
+  // After loading through initMetrics (which should dedup), totals should be correct
+  const tmpBase = mkdtempSync(join(tmpdir(), "gsd-metrics-cost-inflation-"));
+  mkdirSync(join(tmpBase, ".gsd"), { recursive: true });
+  try {
+    resetMetrics();
+    writeFileSync(
+      join(tmpBase, ".gsd", "metrics.json"),
+      JSON.stringify({ version: 1, projectStartedAt: 1700000000000, units: duplicateUnits }, null, 2),
+    );
+    initMetrics(tmpBase);
+    const ledger = getLedger()!;
+    const dedupedTotals = getProjectTotals(ledger.units);
+    assert.equal(ledger.units.length, 1, "20 duplicates should collapse to 1 entry");
+    assert.equal(
+      dedupedTotals.cost, lastEntryCost,
+      `deduped cost should be ${lastEntryCost}, not ${dedupedTotals.cost}`,
+    );
+  } finally {
+    resetMetrics();
+    rmSync(tmpBase, { recursive: true, force: true });
+  }
+});