diff --git a/drivers/stream-sandbox.ts b/drivers/stream-sandbox.ts
index 31ce654..b62942a 100644
--- a/drivers/stream-sandbox.ts
+++ b/drivers/stream-sandbox.ts
@@ -134,6 +134,11 @@ export interface StreamHealth {
   costUsd: number | null
   /** Tokens the agent says it has spent, or null when it did not say. */
   tokens: number | null
+  /** Input and output tokens apart, and turns taken. A ratio is diagnostic:
+   *  1.8M in against 72 out is an agent reading, not one writing. */
+  inputTokens: number | null
+  outputTokens: number | null
+  turns: number | null
   /**
    * Which credential path the agent used, as its launcher reported it.
    *
@@ -408,16 +413,30 @@ export function createStreamSandboxDriver(options: StreamSandboxDriverOptions):
    * Written when the agent exits, so it is absent for a cell read while the
    * agent still runs. Absence is reported as absence.
    */
-  function reportedMeter(): { costUsd: number | null; tokens: number | null; authMode: 'api-key' | 'oauth' | null } {
+  function reportedMeter(): {
+    costUsd: number | null
+    tokens: number | null
+    inputTokens: number | null
+    outputTokens: number | null
+    turns: number | null
+    authMode: 'api-key' | 'oauth' | null
+  } {
     const nonNegative = (value: unknown): number | null =>
       typeof value === 'number' && Number.isFinite(value) && value >= 0 ? value : null
     try {
       const parsed: unknown = JSON.parse(readFileSync(join(dir, 'agent-cost.json'), 'utf8'))
-      const meter = parsed as { usd?: unknown; tokens?: unknown; authMode?: unknown }
+      const meter = parsed as Record<string, unknown>
       const mode = meter.authMode === 'api-key' || meter.authMode === 'oauth' ? meter.authMode : null
-      return { costUsd: nonNegative(meter.usd), tokens: nonNegative(meter.tokens), authMode: mode }
+      return {
+        costUsd: nonNegative(meter.usd),
+        tokens: nonNegative(meter.tokens),
+        inputTokens: nonNegative(meter.inputTokens),
+        outputTokens: nonNegative(meter.outputTokens),
+        turns: nonNegative(meter.turns),
+        authMode: mode,
+      }
     } catch {
-      return { costUsd: null, tokens: null, authMode: null }
+      return { costUsd: null, tokens: null, inputTokens: null, outputTokens: null, turns: null, authMode: null }
     }
   }
 
diff --git a/examples/arena/airstriker.matrix b/examples/arena/airstriker.matrix
new file mode 100644
index 0000000..f3f6a65
--- /dev/null
+++ b/examples/arena/airstriker.matrix
@@ -0,0 +1,17 @@
+# airstriker on the arena board. The clock and seed are the ones this game's packaged
+# reference was recorded at; any other value makes its contract underivable.
+#
+# Two axes vary, not one. `buildMin` asks whether more time to BUILD produces a
+# better player, which is a different question from which model is stronger and
+# the one an efficiency study actually needs.
+profile.opus-3    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=3 transport=persistent
+profile.opus-8    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=8 transport=persistent
+profile.sonnet-3  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=3 transport=persistent
+profile.sonnet-8  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=8 transport=persistent
+
+game.sky adapter=stable-retro target=Airstriker-Genesis
+objective.score goal=maximize:score horizon=2000 budgetUsd=4
+protocol.det frameskip=4 sticky=0 seeds=1
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/arena/breakout.matrix b/examples/arena/breakout.matrix
new file mode 100644
index 0000000..57fc716
--- /dev/null
+++ b/examples/arena/breakout.matrix
@@ -0,0 +1,17 @@
+# breakout on the arena board. The clock and seed are the ones this game's packaged
+# reference was recorded at; any other value makes its contract underivable.
+#
+# Two axes vary, not one. `buildMin` asks whether more time to BUILD produces a
+# better player, which is a different question from which model is stronger and
+# the one an efficiency study actually needs.
+profile.opus-3    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=3 transport=persistent
+profile.opus-8    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=8 transport=persistent
+profile.sonnet-3  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=3 transport=persistent
+profile.sonnet-8  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=8 transport=persistent
+
+game.brick adapter=ale target=breakout
+objective.score goal=maximize:score horizon=3000 budgetUsd=4
+protocol.det frameskip=4 sticky=0 seeds=1
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/arena/cartpole.matrix b/examples/arena/cartpole.matrix
new file mode 100644
index 0000000..10c44f4
--- /dev/null
+++ b/examples/arena/cartpole.matrix
@@ -0,0 +1,17 @@
+# cartpole on the arena board. The clock and seed are the ones this game's packaged
+# reference was recorded at; any other value makes its contract underivable.
+#
+# Two axes vary, not one. `buildMin` asks whether more time to BUILD produces a
+# better player, which is a different question from which model is stronger and
+# the one an efficiency study actually needs.
+profile.opus-3    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=3 transport=persistent
+profile.opus-8    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=8 transport=persistent
+profile.sonnet-3  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=3 transport=persistent
+profile.sonnet-8  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=8 transport=persistent
+
+game.pole adapter=gymnasium target=CartPole-v1
+objective.steps goal=maximize:steps horizon=500 budgetUsd=4
+protocol.det frameskip=1 sticky=0 seeds=1 seed0=7
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/arena/frozenlake.matrix b/examples/arena/frozenlake.matrix
new file mode 100644
index 0000000..5b2365d
--- /dev/null
+++ b/examples/arena/frozenlake.matrix
@@ -0,0 +1,17 @@
+# frozenlake on the arena board. The clock and seed are the ones this game's packaged
+# reference was recorded at; any other value makes its contract underivable.
+#
+# Two axes vary, not one. `buildMin` asks whether more time to BUILD produces a
+# better player, which is a different question from which model is stronger and
+# the one an efficiency study actually needs.
+profile.opus-3    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=3 transport=persistent
+profile.opus-8    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=8 transport=persistent
+profile.sonnet-3  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=3 transport=persistent
+profile.sonnet-8  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=8 transport=persistent
+
+game.ice adapter=gymnasium target=FrozenLake-v1
+objective.goal goal=maximize:steps horizon=200 budgetUsd=4
+protocol.det frameskip=1 sticky=0 seeds=1 seed0=3
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/arena/puzzle.matrix b/examples/arena/puzzle.matrix
new file mode 100644
index 0000000..de285be
--- /dev/null
+++ b/examples/arena/puzzle.matrix
@@ -0,0 +1,17 @@
+# puzzle on the arena board. The clock and seed are the ones this game's packaged
+# reference was recorded at; any other value makes its contract underivable.
+#
+# Two axes vary, not one. `buildMin` asks whether more time to BUILD produces a
+# better player, which is a different question from which model is stronger and
+# the one an efficiency study actually needs.
+profile.opus-3    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=3 transport=persistent
+profile.opus-8    harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=8 transport=persistent
+profile.sonnet-3  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=3 transport=persistent
+profile.sonnet-8  harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=8 transport=persistent
+
+game.puzzle adapter=native-2048 target=2048
+objective.score goal=maximize:score horizon=20000 budgetUsd=4
+protocol.det frameskip=1 sticky=0 seeds=1
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/board/airstriker.matrix b/examples/board/airstriker.matrix
new file mode 100644
index 0000000..b3782d9
--- /dev/null
+++ b/examples/board/airstriker.matrix
@@ -0,0 +1,11 @@
+# airstriker: one game of the board. Its clock and seed are the ones its packaged
+# reference was recorded at; any other value makes the contract underivable.
+profile.cycler harness=none policy=./examples/policies/cycler.mjs note=cycles-the-stated-vocabulary
+profile.masher harness=none policy=./examples/policies/masher.mjs note=one-word-baseline
+
+game.sky adapter=stable-retro target=Airstriker-Genesis
+objective.score goal=maximize:score horizon=300 budgetUsd=1
+protocol.det frameskip=4 sticky=0 seeds=1
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/board/breakout.matrix b/examples/board/breakout.matrix
new file mode 100644
index 0000000..d7e4bb2
--- /dev/null
+++ b/examples/board/breakout.matrix
@@ -0,0 +1,11 @@
+# breakout: one game of the board. Its clock and seed are the ones its packaged
+# reference was recorded at; any other value makes the contract underivable.
+profile.cycler harness=none policy=./examples/policies/cycler.mjs note=cycles-the-stated-vocabulary
+profile.masher harness=none policy=./examples/policies/masher.mjs note=one-word-baseline
+
+game.brick adapter=ale target=breakout
+objective.score goal=maximize:score horizon=300 budgetUsd=1
+protocol.det frameskip=4 sticky=0 seeds=1
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/board/cartpole.matrix b/examples/board/cartpole.matrix
new file mode 100644
index 0000000..a1714b7
--- /dev/null
+++ b/examples/board/cartpole.matrix
@@ -0,0 +1,11 @@
+# cartpole: one game of the board. Its clock and seed are the ones its packaged
+# reference was recorded at; any other value makes the contract underivable.
+profile.cycler harness=none policy=./examples/policies/cycler.mjs note=cycles-the-stated-vocabulary
+profile.masher harness=none policy=./examples/policies/masher.mjs note=one-word-baseline
+
+game.pole adapter=gymnasium target=CartPole-v1
+objective.steps goal=maximize:steps horizon=200 budgetUsd=1
+protocol.det frameskip=1 sticky=0 seeds=1 seed0=7
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/board/frozenlake.matrix b/examples/board/frozenlake.matrix
new file mode 100644
index 0000000..fb01bb2
--- /dev/null
+++ b/examples/board/frozenlake.matrix
@@ -0,0 +1,11 @@
+# frozenlake: one game of the board. Its clock and seed are the ones its packaged
+# reference was recorded at; any other value makes the contract underivable.
+profile.cycler harness=none policy=./examples/policies/cycler.mjs note=cycles-the-stated-vocabulary
+profile.masher harness=none policy=./examples/policies/masher.mjs note=one-word-baseline
+
+game.ice adapter=gymnasium target=FrozenLake-v1
+objective.goal goal=maximize:steps horizon=100 budgetUsd=1
+protocol.det frameskip=1 sticky=0 seeds=1 seed0=3
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/board/puzzle.matrix b/examples/board/puzzle.matrix
new file mode 100644
index 0000000..3bf000a
--- /dev/null
+++ b/examples/board/puzzle.matrix
@@ -0,0 +1,11 @@
+# puzzle: one game of the board. Its clock and seed are the ones its packaged
+# reference was recorded at; any other value makes the contract underivable.
+profile.cycler harness=none policy=./examples/policies/cycler.mjs note=cycles-the-stated-vocabulary
+profile.masher harness=none policy=./examples/policies/masher.mjs note=one-word-baseline
+
+game.puzzle adapter=native-2048 target=2048
+objective.score goal=maximize:score horizon=300 budgetUsd=1
+protocol.det frameskip=1 sticky=0 seeds=1
+sensor.ascii pixels=off channels=-
+
+reps 1
diff --git a/examples/policies/masher.mjs b/examples/policies/masher.mjs
index d379ccc..8b6093d 100755
--- a/examples/policies/masher.mjs
+++ b/examples/policies/masher.mjs
@@ -1,5 +1,11 @@
 #!/usr/bin/env node
-// A trivial baseline: one word, always. It is what a real arm has to beat.
+// Plays the first word the game states, forever: the weakest honest baseline.
+//
+// It used to emit a hardcoded lowercase word. On ALE Breakout, whose words are
+// NOOP, FIRE, RIGHT and LEFT, every one was illegal and substituted, and the
+// first decision spent ten seconds reaching a driver timeout. A control that
+// cannot name a legal move measures the harness, not the game.
+const FALLBACK = 'up'
 let buffer = ''
 process.stdin.setEncoding('utf8')
 process.stdin.on('data', (chunk) => {
@@ -7,7 +13,16 @@ process.stdin.on('data', (chunk) => {
   for (;;) {
     const at = buffer.indexOf('\n')
     if (at < 0) break
+    const line = buffer.slice(0, at)
     buffer = buffer.slice(at + 1)
-    process.stdout.write('up\n')
+    let word = FALLBACK
+    try {
+      const request = JSON.parse(line)
+      if (Array.isArray(request.commands) && request.commands.length > 0) word = request.commands[0]
+    } catch {
+      // An unreadable request is still a request. Answering keeps the episode
+      // gradeable instead of stalling it at a timeout.
+    }
+    process.stdout.write(`${word}\n`)
   }
 })
diff --git a/examples/transfer-agents-2048.matrix b/examples/transfer-agents-2048.matrix
new file mode 100644
index 0000000..214d92a
--- /dev/null
+++ b/examples/transfer-agents-2048.matrix
@@ -0,0 +1,12 @@
+# Half of a two-game transfer study, played by real profiles.
+#
+# The cheap controls tie at 0 on Breakout, and two tied players have no order,
+# so a rank correlation has nothing to correlate. These build a player instead.
+profile.opus   harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=6 transport=persistent
+profile.sonnet harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=6 transport=persistent
+
+game.puzzle adapter=native-2048 target=2048
+objective.score goal=maximize:score horizon=20000 budgetUsd=4
+protocol.det frameskip=1 sticky=0 seeds=1 queue=8 empty=noop pace=0
+sensor.ascii pixels=off channels=-
+reps 2
diff --git a/examples/transfer-agents-breakout.matrix b/examples/transfer-agents-breakout.matrix
new file mode 100644
index 0000000..17bea58
--- /dev/null
+++ b/examples/transfer-agents-breakout.matrix
@@ -0,0 +1,10 @@
+# The other half. frameskip 4 is the clock Breakout's packaged reference was
+# recorded at; any other value makes its contract underivable.
+profile.opus   harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-opus-5   buildMin=6 transport=persistent
+profile.sonnet harness=./harnesses/claude-code author=./harnesses/author-policy model=claude-sonnet-5 buildMin=6 transport=persistent
+
+game.brick adapter=ale target=breakout
+objective.score goal=maximize:score horizon=3000 budgetUsd=4
+protocol.det frameskip=4 sticky=0 seeds=1 queue=8 empty=noop pace=0
+sensor.ascii pixels=off channels=-
+reps 2
diff --git a/matrix-run.ts b/matrix-run.ts
index c62b6a6..dd69d5b 100644
--- a/matrix-run.ts
+++ b/matrix-run.ts
@@ -156,6 +156,17 @@ export interface CellResult {
      */
     authMode: 'api-key' | 'oauth' | null
   } | null
+  /**
+   * Everything the run measured that a single number cannot carry.
+   *
+   * A row answers "how did it do". This answers "what happened", which is the
+   * question every autopsy in this work has actually needed. The data was
+   * always collected and then discarded at this boundary: `latencyMs` is a full
+   * per-decision array, the evidence watcher holds every channel at every
+   * decision, and driver health is a structured record that was being flattened
+   * into one sentence of prose.
+   */
+  telemetry: CellTelemetry | null
   scoreField: string | null
   /** Which way is better on that channel. A minimize goal ranks inverted. */
   scoreDirection: 'maximize' | 'minimize' | null
@@ -423,6 +434,9 @@ export function blockedResult(cell: MatrixCell, reason: BlockedReason, detail: s
     tokens: null,
     usd: 0,
     build: null,
+    // A cell that never played measured nothing. Null, not an empty spread: an
+    // absent distribution and one with no spread are different facts.
+    telemetry: null,
     // A blocked cell still states what it WOULD have scored on, so a reader can
     // see that an excluded row and a played row were aimed at the same channel.
     scoreField: null,
@@ -498,6 +512,8 @@ export async function runCell(cell: MatrixCell, options: RunCellOptions = {}): P
   // practice game nobody scores, and the program it leaves behind is what the
   // scored episode actually runs. The agent is not running by then.
   let authored: CellResult['build'] = null
+  /** Build-phase token split, kept apart from the row's headline totals. */
+  let authoredDetail: { inputTokens: number | null; outputTokens: number | null; turns: number | null } | null = null
   let policyCommand: string | null = null
   if (cell.profile.author !== undefined) {
     const attempt = await authorPolicy(cell, options, now)
@@ -508,6 +524,7 @@ export async function runCell(cell: MatrixCell, options: RunCellOptions = {}): P
       policy: attempt.policy,
       authMode: attempt.authMode,
     }
+    authoredDetail = attempt.detailTokens
     if (attempt.policy === null) {
       // Blocked, never scored zero. A profile that built nothing did not play
       // badly; it produced no player, and those are different findings.
@@ -553,6 +570,8 @@ export async function runCell(cell: MatrixCell, options: RunCellOptions = {}): P
     const watched = watchEvidence(built.game)
     let record: EpisodeRecord
     let actionsHash: string | null
+    /** Every word the driver played, in order, for the raw trace. */
+    let actions: readonly string[] = []
     try {
       const played = await playEpisode(
         watched.game,
@@ -566,6 +585,7 @@ export async function runCell(cell: MatrixCell, options: RunCellOptions = {}): P
       )
       record = played.record
       actionsHash = played.log.head()
+      actions = played.log.inputs()
     } catch (error) {
       return blockedResult(cell, 'episode-failed', (error as Error).message, now() - started)
     }
@@ -590,6 +610,33 @@ export async function runCell(cell: MatrixCell, options: RunCellOptions = {}): P
       usd: meter.metered && meter.costUsd === null ? null : (meter.costUsd ?? 0) + record.spentUsd,
       authMode: meter.authMode,
       build: authored,
+      telemetry: {
+        latencyMs: spreadOf(record.latencyMs),
+        scoreSeries: spreadOf(channel(watched.snapshots, goal.field)),
+        channelsLast: watched.snapshots[watched.snapshots.length - 1] ?? {},
+        inputs: {
+          total: record.inputStats.inputs,
+          distinct: Math.round(record.inputStats.uniqueRatio * record.inputStats.inputs),
+          uniqueRatio: record.inputStats.uniqueRatio,
+        },
+        milestones: built.contract.milestones.map((milestone) => ({
+          id: milestone.id,
+          verified: record.verified.includes(milestone.id),
+        })),
+        health: healthOf(driver),
+        build: authoredDetail,
+        // The evidence watcher records the state BEFORE the first input as
+        // snapshot 0, so decision n is snapshot n+1. Off by one here would
+        // attribute every outcome to the input before the one that caused it.
+        trace: actions.map((input: string, i: number) => ({
+          turn: i + 1,
+          input,
+          latencyMs: record.latencyMs[i] ?? null,
+          channels: watched.snapshots[i + 1] ?? {},
+        })),
+        budgetExhausted: record.budgetExhausted,
+        spentUsd: record.spentUsd,
+      },
       cleared: record.gameOver,
       verified: record.verified,
       milestones: record.score,
@@ -692,6 +739,7 @@ async function authorPolicy(
   minutes: number
   policy: string | null
   authMode: 'api-key' | 'oauth' | null
+  detailTokens: { inputTokens: number | null; outputTokens: number | null; turns: number | null }
   detail: string | null
 }> {
   const profile = cell.profile
@@ -717,6 +765,7 @@ async function authorPolicy(
       minutes: 0,
       policy: null,
       authMode: null,
+      detailTokens: { inputTokens: null, outputTokens: null, turns: null },
       detail: `no practice game: ${(error as Error).message}`,
     }
   }
@@ -787,16 +836,130 @@ async function authorPolicy(
       ? 'the agent left a policy that is not executable'
       : 'the agent left no policy'
   }
+  const full = healthOf(driver) ?? {}
+  const num = (v: unknown): number | null => (typeof v === 'number' && Number.isFinite(v) ? v : null)
   return {
     usd: meter.costUsd,
     tokens: meter.tokens,
     authMode: meter.authMode,
+    detailTokens: {
+      inputTokens: num(full.inputTokens),
+      outputTokens: num(full.outputTokens),
+      turns: num(full.turns),
+    },
     minutes: (now() - started) / 60_000,
     policy,
     detail,
   }
 }
 
+/** One decision, as it happened. */
+export interface DecisionTrace {
+  turn: number
+  /** The word the driver emitted and the game accepted. */
+  input: string
+  /** Wall clock this decision took, in milliseconds. */
+  latencyMs: number | null
+  /** Every evidence channel after the input was applied. */
+  channels: Record<string, number>
+}
+
+/** A distribution, reported so a reader can see shape rather than a mean. */
+export interface Spread {
+  n: number
+  min: number
+  p50: number
+  p90: number
+  p99: number
+  max: number
+  mean: number
+  /** Equal-width buckets over [min, max], for a histogram. Empty when n < 2. */
+  histogram: { from: number; to: number; count: number }[]
+}
+
+/** What one cell measured beyond its headline number. */
+export interface CellTelemetry {
+  /** Wall clock per decision, in milliseconds. */
+  latencyMs: Spread | null
+  /** The scored channel at every decision, so a trajectory is visible. */
+  scoreSeries: Spread | null
+  /** Every evidence channel this game published, and its last value. */
+  channelsLast: Record<string, number>
+  /** Inputs the driver emitted, and how varied they were. */
+  inputs: { total: number; distinct: number; uniqueRatio: number }
+  /** Per-milestone cost, as the contract recorded it. */
+  milestones: { id: string; verified: boolean }[]
+  /** The transport's own record, structured rather than prose. */
+  health: Record<string, unknown> | null
+  /** Build-phase detail when the profile authored its player. */
+  build: { inputTokens: number | null; outputTokens: number | null; turns: number | null } | null
+  /**
+   * Every decision, raw, in the order it happened.
+   *
+   * A summary answers "what shape"; this answers "what happened at decision
+   * 811", which is the question every autopsy in this work has ended up
+   * asking. Each entry carries the turn, the word played, that decision's
+   * latency, and every evidence channel as it stood afterwards.
+   *
+   * It is the whole episode, so a caller writing it to disk should put it
+   * beside the row rather than inside it.
+   */
+  trace: DecisionTrace[]
+  /**
+   * Where the trace was written, when a runner moved it out of the row.
+   *
+   * Null while it is still inline. A reader that finds `trace` empty and this
+   * set knows the decisions exist rather than that there were none.
+   */
+  tracePath?: string
+  budgetExhausted: boolean
+  spentUsd: number
+}
+
+/**
+ * Summarise a series without hiding its shape.
+ *
+ * A mean alone has hidden every interesting result in this work: opus looked
+ * consistent to 0.2% at a censored horizon and varied 5.3x uncensored. Quantiles
+ * and a histogram make that visible on the row instead of in a later autopsy.
+ */
+export function spreadOf(values: readonly number[], buckets = 12): Spread | null {
+  if (values.length === 0) return null
+  const sorted = [...values].sort((a, b) => a - b)
+  const at = (q: number): number => sorted[Math.min(sorted.length - 1, Math.floor(q * sorted.length))]!
+  const min = sorted[0]!
+  const max = sorted[sorted.length - 1]!
+  const histogram: { from: number; to: number; count: number }[] = []
+  if (sorted.length > 1 && max > min) {
+    const width = (max - min) / buckets
+    for (let i = 0; i < buckets; i += 1) {
+      const from = min + i * width
+      const to = i === buckets - 1 ? max : from + width
+      histogram.push({
+        from,
+        to,
+        count: sorted.filter((v) => v >= from && (i === buckets - 1 ? v <= to : v < to)).length,
+      })
+    }
+  }
+  return {
+    n: sorted.length,
+    min,
+    p50: at(0.5),
+    p90: at(0.9),
+    p99: at(0.99),
+    max,
+    mean: sorted.reduce((a, b) => a + b, 0) / sorted.length,
+    histogram,
+  }
+}
+
+/** Read a driver's own health record, whatever transport it is. */
+function healthOf(driver: AgentDriver): Record<string, unknown> | null {
+  const reporter = driver as { health?: () => Record<string, unknown> }
+  return typeof reporter.health === 'function' ? reporter.health() : null
+}
+
 function meterOf(driver: AgentDriver): {
   metered: boolean
   costUsd: number | null
diff --git a/matrix.mts b/matrix.mts
index 589a25d..3036615 100644
--- a/matrix.mts
+++ b/matrix.mts
@@ -11,8 +11,8 @@
  * Env knobs:
  *   PLAYPROOF_PYTHON   interpreter that runs an emulator worker (default python3)
  */
-import { mkdir, readFile, writeFile } from 'node:fs/promises'
-import { dirname } from 'node:path'
+import { copyFile, mkdir, readdir, readFile, stat, writeFile } from 'node:fs/promises'
+import { dirname, join } from 'node:path'
 import { cellName, enumerateCells, parseMatrix } from './matrix'
 import { assertJoinable, blockedResult, effectiveArms, generalization, runCell, type CellResult } from './matrix-run'
 
@@ -116,6 +116,41 @@ for (const [index, cell] of cells.entries()) {
   } finally {
     clearInterval(heartbeat)
   }
+  // Keep what the cell produced. The authoring sandbox is a temp directory
+  // that is reclaimed, so the program an agent wrote and the transcript of how
+  // it wrote it are lost the moment the run ends. Those are the two artifacts
+  // an autopsy of a build actually needs.
+  if (row.build?.policy != null && outPath !== undefined) {
+    const keep = join(dirname(outPath), 'artifacts', cellName(cell).replace(/[^\w.-]+/gu, '_'))
+    try {
+      await mkdir(keep, { recursive: true })
+      const from = dirname(row.build.policy)
+      for (const name of await readdir(from)) {
+        // Observation files are the game talking, not the agent working, and a
+        // practice run writes thousands of them.
+        if (name === 'observations' || name === 'latest.json') continue
+        const source = join(from, name)
+        if ((await stat(source)).isDirectory()) continue
+        await copyFile(source, join(keep, name))
+      }
+    } catch (error) {
+      console.error(`[${index + 1}/${cells.length}] could not keep artifacts: ${(error as Error).message}`)
+    }
+  }
+  // The raw trace is the whole episode. It goes beside the artifact as JSONL,
+  // one decision per line, so the row stays readable and nothing is lost: a
+  // 20,000-decision run would otherwise make the study file unopenable.
+  if (row.telemetry !== null && row.telemetry.trace.length > 0 && outPath !== undefined) {
+    const slug = cellName(cell).replace(/[^\w.-]+/gu, '_')
+    const tracePath = join(dirname(outPath), 'traces', `${slug}.jsonl`)
+    try {
+      await mkdir(dirname(tracePath), { recursive: true })
+      await writeFile(tracePath, row.telemetry.trace.map((d) => JSON.stringify(d)).join('\n') + '\n')
+      row.telemetry = { ...row.telemetry, trace: [], tracePath }
+    } catch (error) {
+      console.error(`[${index + 1}/${cells.length}] could not write the trace: ${(error as Error).message}`)
+    }
+  }
   rows.push(row)
   const headline = row.status === 'played'
     ? `score=${row.score ?? '-'} deaths=${row.deaths ?? '-'} decisions=${row.decisions}`