UiPath
diff --git a/‎.claude/harness-candidates.md‎
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diff --git a/‎.github/workflows/pr-checks.yml‎
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diff --git a/‎CLAUDE.md‎
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diff --git a/‎docs/agents/HARNESS_PARITY.md‎
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diff --git a/‎evalboard/app/runs/[id]/[...task]/__tests__/message-timeline.test.tsx‎
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diff --git a/‎evalboard/app/runs/[id]/[...task]/_sections.tsx‎
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diff --git a/‎evalboard/app/runs/[id]/[...task]/page.tsx‎
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diff --git a/‎evalboard/lib/__tests__/harnessOverhead.test.ts‎
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@@ -593,6 +593,21 @@ jobs:
           test "$FAILED" = "0" || { echo "smoke-pass had unexpected failures"; exit 1; }
           test "$ERRORED" = "0" || { echo "smoke-pass had errors"; exit 1; }
 
+      # The four wall-clock buckets (head + generation + UNION(tool) + tail)
+      # must account for each turn's own duration. This is the TWO-SIDED gate:
+      # the committed golden sensor only catches an OVERSHOOT, so a bucket that
+      # claims LESS time than it should — the defect class this area keeps
+      # producing — passes every test in the suite. It needs live task.json
+      # files, which the smoke-pass run above already leaves on disk.
+      #
+      # COVERS CLAUDE-CODE ONLY: experiments/default.yaml sets type: claude-code,
+      # so every turn here is that harness. The other four are covered by
+      # tests/test_timing_identity_contract.py, which is ms-exact but synthetic.
+      - name: Verify timing residual (claude-code only)
+        run: |
+          .venv/bin/python scripts/timing/decompose_run.py \
+            $(find runs/ci-smoke-pass -name task.json) --max-residual-pct 5
+
       - name: Verify smoke-fail bucket
         run: |
           F=runs/ci-smoke-fail/experiment.json
 
@@ -13,7 +13,7 @@ import type {
     TokenTotals,
     ToolCall,
 } from "@/lib/runs";
-import { toolExecutionMs } from "@/lib/timing";
+import { measuredToolExecutionMs, toolExecutionMs } from "@/lib/timing";
 import {
     type PerMessageImpact,
     buildThinkingModel,
@@ -318,6 +318,11 @@ export function MessageTimelineSection({
     subAgentUsageByToolId = {},
     impactByIndex,
     taskDurationSeconds,
+    harnessStartupMs,
+    harnessTeardownMs,
+    storedToolMs,
+    setupMs,
+    gradingMs,
 }: {
     messages: MessageEvent[];
     // Per-Agent-call sub-agent token breakdown (input/output/cache-create/
@@ -332,6 +337,31 @@ export function MessageTimelineSection({
     // tool execution do NOT account for. Null/absent on a run predating
     // duration capture — the cell then renders "—" rather than a fake residual.
     taskDurationSeconds?: number | null;
+    // The turn-level head and tail, summed over the task's turns: wall clock
+    // before the first generation window opened and after the last one closed.
+    // Turn-scoped, so they cannot be derived from the per-message stream the
+    // other stats come from. Null/absent on a run predating the capture, and
+    // the cells then read "—" while Unaccounted keeps exactly its old meaning.
+    harnessStartupMs?: number | null;
+    harnessTeardownMs?: number | null;
+    // The tool bucket as the HARNESS recorded it, summed over the task's turns
+    // (`TurnRecord.tool_union_ms`). Preferred over recomputing it from the
+    // message stream, because the collector wrote it from the same span set it
+    // measured the head and the tail against — reading it is how this cell and
+    // the harness are guaranteed to agree rather than merely observed to.
+    // Null/absent on a run predating the field, and the cell then computes the
+    // union itself; the two agree by construction, since `toolExecutionMs`
+    // applies the same bounded-spans-only policy as the Python selector.
+    storedToolMs?: number | null;
+    // TASK-scoped phases either side of the turns: provisioning before the
+    // first turn, criteria checking after the last. Named so Unaccounted is a
+    // residual instead of a label for the setup phase — it was ~1.9s of known,
+    // constant orchestrator cost on every row, which reads as 10% of a 19s
+    // task and would read 60% of a 3s one. Null/absent on a run predating the
+    // capture, and the cells then read "—" while Unaccounted keeps exactly its
+    // old meaning.
+    setupMs?: number | null;
+    gradingMs?: number | null;
 }) {
     // Token columns can be shown as counts or as their estimated USD value.
     const [unit, setUnit] = useState<Unit>("tokens");
@@ -381,7 +411,17 @@ export function MessageTimelineSection({
     // occupy the wall clock once. Summing them made Unaccounted negative on
     // any task that ran tools in parallel, reporting overlap as if the
     // harness had lost time.
-    const toolExecMs = toolExecutionMs(mainThread);
+    //
+    // STORED first, computed as the fallback. `?? null` and not `??  computed`
+    // in one expression because `storedToolMs` of 0 is a measurement and must
+    // win: the harness recorded spans and they occupied no measurable time.
+    // Only its ABSENCE (a run predating the field) routes here.
+    //
+    // The Generation cell below has no stored twin and is deliberately still
+    // computed from the messages — the reconciliation entry exists so a
+    // consumer sums that stream rather than reading a separate aggregate. The
+    // mixed sourcing is intentional; see `sumTurnBuckets` in lib/runs.ts.
+    const toolExecMs = storedToolMs ?? measuredToolExecutionMs(mainThread);
     const slowGen = mainThread.filter(
         (m) => (m.generationMs ?? 0) >= SLOW_GEN_MS,
     ).length;
@@ -398,11 +438,25 @@ export function MessageTimelineSection({
     const attributableGenMs = totalGenMs - mixedMs;
     const thinkingShare = attributableGenMs > 0 ? thinkingMs / attributableGenMs : 0;
 
-    // Wall clock the agent stream does not explain. Negative means generation
-    // and tool execution overlapped, which is a real signal — never clamped.
+    // Wall clock the agent stream does not explain, AFTER every named bucket.
+    // Startup and teardown are subtracted because they are measured intervals,
+    // not residual — leaving them in reported a harness's CLI boot as
+    // unexplained time. `?? 0` subtracts only what was actually measured, so an
+    // older run with neither field keeps exactly its previous number.
+    // Negative means generation and tool execution overlapped, which is a real
+    // signal — never clamped.
     const taskMs =
         taskDurationSeconds != null ? taskDurationSeconds * 1000 : null;
-    const unaccountedMs = taskMs != null ? taskMs - totalGenMs - toolExecMs : null;
+    const unaccountedMs =
+        taskMs != null
+            ? taskMs -
+              totalGenMs -
+              (toolExecMs ?? 0) -
+              (harnessStartupMs ?? 0) -
+              (harnessTeardownMs ?? 0) -
+              (setupMs ?? 0) -
+              (gradingMs ?? 0)
+            : null;
     const unaccountedShare =
         taskMs != null && taskMs > 0 && unaccountedMs != null
             ? unaccountedMs / taskMs
@@ -419,19 +473,36 @@ export function MessageTimelineSection({
             <p className="text-[10px] text-gray-500">
                 MIXED = multiple block types · red = slow (gen ≥10s, tool ≥5s)
             </p>
-            {/* TWO LEVELS, two rows. The top row's Generation, Tool exec and
-                Unaccounted sum to the task's wall clock; the bottom row splits
-                Generation alone and sums to IT. Rendering the split as a
-                sub-cell of one top-row cell put both sums on one line, where
-                nothing said which total each part belonged to. */}
+            {/* TWO LEVELS, two rows. The top row's five time cells — Startup,
+                Generation, Tool exec, Teardown, Unaccounted — sum to the task's
+                wall clock; the bottom row splits Generation alone and sums to
+                IT. Rendering the split as a sub-cell of one top-row cell put
+                both sums on one line, where nothing said which total each part
+                belonged to. The time cells are ordered as the turn runs. */}
             <div className="bg-gray-50 border border-gray-200 rounded-lg p-3 tabular-nums space-y-3">
-                <div className="grid grid-cols-2 md:grid-cols-5 gap-3 text-xs">
+                <div className="grid grid-cols-2 md:grid-cols-4 lg:grid-cols-5 xl:grid-cols-9 gap-3 text-xs">
                     <div>
                         <div className="text-gray-500 uppercase tracking-wide text-[10px]">
                             Messages
                         </div>
                         <div className="text-gray-900 font-medium">{messageCount}</div>
                     </div>
+                    <div title="sandbox provisioning, agent start() and pre_run — everything before the first turn begins. TASK-scoped, so it is NOT one of the turn's four buckets: those tile a single turn and their identity is asserted to the millisecond, while this happens once for a task that may run many turns. It is the orchestrator's own cost, not the harness's — measured at ~1.9s for claude-code and pi alike. Blank on runs recorded before the field existed.">
+                        <div className="text-gray-500 uppercase tracking-wide text-[10px]">
+                            Setup
+                        </div>
+                        <div className="text-gray-900 font-medium">
+                            {fmtMs(setupMs ?? null)}
+                        </div>
+                    </div>
+                    <div title="wall clock from the turn starting until the harness first observed model output — a latency that INCLUDES time-to-first-token, and the same instant its first generation window opens. Named for the interval it measures, not for what it contains. Deliberately NOT decomposed further: a harness with a CLI to boot fuses CLI boot, provider resolution, dispatch and TTFT here, and no stream carries a marker between them. See docs/agents/HARNESS_PARITY.md.">
+                        <div className="text-gray-500 uppercase tracking-wide text-[10px]">
+                            Startup
+                        </div>
+                        <div className="text-gray-900 font-medium">
+                            {fmtMs(harnessStartupMs ?? null)}
+                        </div>
+                    </div>
                     <div title="model-generation time, split per block kind on the row below">
                         <div className="text-gray-500 uppercase tracking-wide text-[10px]">
                             Generation
@@ -445,10 +516,26 @@ export function MessageTimelineSection({
                             Tool exec
                         </div>
                         <div className="text-gray-900 font-medium">
-                            {fmtMs(toolExecMs)}
+                            {fmtMs(toolExecMs ?? null)}
+                        </div>
+                    </div>
+                    <div title="wall clock after the last generation window closed: SDK/CLI finalization, result assembly and process teardown">
+                        <div className="text-gray-500 uppercase tracking-wide text-[10px]">
+                            Teardown
+                        </div>
+                        <div className="text-gray-900 font-medium">
+                            {fmtMs(harnessTeardownMs ?? null)}
+                        </div>
+                    </div>
+                    <div title="every success-criteria check this row made, summed — the single-shot check, each dialog turn's check, and the post-failure diagnostic pass. Blank when nothing was graded (coder-eval execute) or on runs recorded before the field existed.">
+                        <div className="text-gray-500 uppercase tracking-wide text-[10px]">
+                            Grading
+                        </div>
+                        <div className="text-gray-900 font-medium">
+                            {fmtMs(gradingMs ?? null)}
                         </div>
                     </div>
-                    <div title="task wall clock minus generation and tool execution — includes sandbox setup, grading, simulator calls, and any time the harness did not report">
+                    <div title="task wall clock minus every named bucket above. A TRUE residual now that setup and grading are measured: it used to hold the ~1.9s setup phase, a known constant reading as unexplained time. What is left is post_run, sandbox cleanup, simulator calls and any interval the harness did not report.">
                         <div className="text-gray-500 uppercase tracking-wide text-[10px]">
                             Unaccounted
                         </div>
@@ -771,13 +858,26 @@ export function CostExplorerSection({
     tokens,
     recordedCostUsd,
     taskDurationSeconds,
+    harnessStartupMs,
+    harnessTeardownMs,
+    storedToolMs,
+    setupMs,
+    gradingMs,
 }: {
     messages: MessageEvent[];
     subAgentUsageByToolId?: Record<string, SubAgentTotals>;
     tokens: TokenTotals;
     recordedCostUsd: number | null;
     // Forwarded verbatim to the timeline's Unaccounted cell.
     taskDurationSeconds?: number | null;
+    // Forwarded verbatim to the timeline's Startup/Teardown cells.
+    harnessStartupMs?: number | null;
+    harnessTeardownMs?: number | null;
+    storedToolMs?: number | null;
+    // Forwarded straight through to MessageTimelineSection — this component
+    // renders it and owns no timing of its own.
+    setupMs?: number | null;
+    gradingMs?: number | null;
 }) {
     const [scale, setScale] = useState(1);
     const [toolScale, setToolScale] = useState(1);
@@ -816,6 +916,11 @@ export function CostExplorerSection({
                 subAgentUsageByToolId={subAgentUsageByToolId}
                 impactByIndex={impactByIndex}
                 taskDurationSeconds={taskDurationSeconds}
+                harnessStartupMs={harnessStartupMs}
+                harnessTeardownMs={harnessTeardownMs}
+                storedToolMs={storedToolMs}
+                setupMs={setupMs}
+                gradingMs={gradingMs}
             />
             {model && tokens.total > 0 && (
                 <section className="space-y-2">
@@ -1445,9 +1550,22 @@ function MessageRow({
     const slowTool = m.toolUses.some((t) => (t.durationMs ?? 0) >= SLOW_TOOL_MS);
     const hasErrorTool = m.toolUses.some((t) => t.isError);
     const preview = summaryPreview(m);
-    // Sum tool exec time for this message — matches the rollup strip.
-    const execMs = m.toolUses.reduce((a, t) => a + (t.durationMs ?? 0), 0);
-    const hasExec = m.toolUses.some((t) => t.durationMs != null);
+    // UNION, not sum — and through the same helper the rollup strip uses, so
+    // the row and the header cannot answer one question two ways. Summing
+    // double-books concurrent calls: one measured antigravity turn issued two
+    // `sleep 2` Bash calls overlapping almost entirely, and this cell read
+    // 4.1s for 2.1s of wall clock — more tool time in one message than the
+    // whole task's Tool exec cell, which is impossible on its face. The old
+    // comment here claimed parity with the strip; that stopped being true when
+    // `toolExecutionMs` was changed to union and this line was not. Expand the
+    // row to see each call's own wall clock: sequential calls still add up to
+    // this number, concurrent ones deliberately do not.
+    // `measured…`, so a row whose calls were TIMED BUT UNBOUNDED reads "—"
+    // rather than "0ms". Under the union policy such a call contributes to no
+    // bucket, and claiming it took no time is the one thing that is certainly
+    // false. This replaces a `durationMs != null` guard, which asked whether
+    // the harness timed anything rather than whether it bounded anything.
+    const execMs = measuredToolExecutionMs([m]);
     // Render full body only when something more than the summary exists.
     const hasBody =
         m.toolUses.length > 0 ||
@@ -1492,7 +1610,7 @@ function MessageRow({
                                 : "text-gray-600")
                         }
                     >
-                        {hasExec ? fmtMs(execMs) : "—"}
+                        {fmtMs(execMs)}
                     </span>
                     <span className="flex items-center gap-2 min-w-0">
                         <span
 
@@ -365,6 +365,11 @@ export default async function TaskPage({
                     tokens={task.tokens}
                     recordedCostUsd={task.totalCostUsd}
                     taskDurationSeconds={task.durationSeconds}
+                    harnessStartupMs={task.harnessStartupMs}
+                    setupMs={task.setupMs}
+                    gradingMs={task.gradingMs}
+                    harnessTeardownMs={task.harnessTeardownMs}
+                    storedToolMs={task.storedToolMs}
                 />
             )}
             <ProviderCallTableSection providerCalls={task.providerCalls} />
 
@@ -0,0 +1,80 @@
+import { promises as fs } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
+
+// End-to-end: the two turn-level timing buckets survive the trip from
+// task.json's `iterations` onto TaskDetail. `sumHarnessOverhead` is unit-tested
+// in runs.test.ts; what only a read off disk can catch is a misspelled raw key,
+// since every TurnEntry field is optional and a typo would just parse as
+// absent. Mirrors providerCalls.test.ts's env-stub + fresh-import pattern.
+const RUN = "2026-01-01_00-00-00";
+const TASK = "demo-task";
+let tmp: string;
+
+async function write(rel: string, body: string): Promise<void> {
+    const abs = path.join(tmp, rel);
+    await fs.mkdir(path.dirname(abs), { recursive: true });
+    await fs.writeFile(abs, body);
+}
+
+async function loadRuns() {
+    vi.resetModules();
+    vi.stubEnv("EVALBOARD_LOCAL_RUNS_DIR", tmp);
+    return import("../runs");
+}
+
+async function writeTask(iterations: unknown[]): Promise<void> {
+    await write(
+        `${RUN}/run.json`,
+        JSON.stringify({
+            run_id: RUN,
+            task_results: [{ task_id: TASK, status: "success" }],
+        }),
+    );
+    await write(
+        `${RUN}/default/${TASK}/00/task.json`,
+        JSON.stringify({ final_status: "success", iterations }),
+    );
+}
+
+beforeEach(async () => {
+    tmp = await fs.mkdtemp(path.join(os.tmpdir(), "evalboard-overhead-"));
+});
+
+afterEach(async () => {
+    vi.unstubAllEnvs();
+    await fs.rm(tmp, { recursive: true, force: true });
+});
+
+describe("readTaskDetail: harness startup/teardown", () => {
+    test("sums both buckets across the task's turns", async () => {
+        await writeTask([
+            { harness_startup_ms: 3047.9, harness_teardown_ms: 33.1 },
+            { harness_startup_ms: 120.5, harness_teardown_ms: 4.2 },
+        ]);
+        const { readTaskDetail } = await loadRuns();
+        const detail = await readTaskDetail(RUN, TASK);
+        expect(detail?.harnessStartupMs).toBeCloseTo(3168.4, 3);
+        expect(detail?.harnessTeardownMs).toBeCloseTo(37.3, 3);
+    });
+
+    test("an older run without the fields reports null, not zero", async () => {
+        await writeTask([{ model_used: "claude-haiku-4-5" }]);
+        const { readTaskDetail } = await loadRuns();
+        const detail = await readTaskDetail(RUN, TASK);
+        expect(detail?.harnessStartupMs).toBeNull();
+        expect(detail?.harnessTeardownMs).toBeNull();
+    });
+
+    test("a measured zero head is preserved as 0", async () => {
+        // A head of 0.0 stays representable: a turn can reach its first model
+        // output with nothing measurable in front of it. It must not read as
+        // "never measured", which is what null means.
+        await writeTask([{ harness_startup_ms: 0.0, harness_teardown_ms: 834.7 }]);
+        const { readTaskDetail } = await loadRuns();
+        const detail = await readTaskDetail(RUN, TASK);
+        expect(detail?.harnessStartupMs).toBe(0);
+        expect(detail?.harnessTeardownMs).toBeCloseTo(834.7, 3);
+    });
+});