=== session s0 transcript ===
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
 for (let i = 0; i < lines.length; i++) {
    const r = lineRows(lines[i]!, cols);
    const c = lines[i]!.length + (i > 0 ? 1 : 0);
    if (headRows + r > headRowBudget || headChars + c > headCharBudget) break;
    headRows += r;
    headChars += c;
    headCut = i + 1;
  }
  if (headCut === 0) headCut = 1;
  let tailRows = 0;
  let tailChars = 0;
  let tailStart = lines.length;
  for (let i = lines.length - 1; i >= headCut; i--) {
    const r = lineRows(lines[i]!, cols);
    const c = lines[i]!.length + (i < lines.length - 1 ? 1 : 0);
    if (tailRows + r > tailRowBudget || tailChars + c > tailCharBudget) break;
    tailRows += r;
    tailChars += c;
    tailStart = i;
  }
  if (tailStart <= headCut || tailStart >= lines.length) {
    const head = lines.slice(0, headCut).join(nlChar);
    const omitted = originalChars - head.length;
    return {
      text:
        head +
        buildPagingMarker({
          originalChars,
          originalLines,
          originalEstImages: estImages,
          shownHeadLines: headCut,
          shownTailLines: 0,
          omittedLines: originalLines - headCut,
          omittedChars: omitted,
        }),
      omittedChars: omitted,
      truncated: true,
    };
  }
  const headText = lines.slice(0, headCut).join(nlChar);
  const tailText = lines.slice(tailStart).join(nlChar);
  const shownChars = headText.length + tailText.length;
  const omitted = originalChars - shownChars;
  return {
    text:
      headText +
      buildPagingMarker({
        originalChars,
        originalLines,
        originalEstImages: estImages,
        shownHeadLines: headCut,
        shownTailLines: lines.length - tailStart,
        omittedLines: originalLines - headCut - (lines.length - tailStart),
        omittedChars: omitted,
      }) +
      tailText,
    omittedChars: omitted,
    truncated: true,
  };
}

async function textToImageBlocks(
  text: string,
  cols: number,
  numCols: number = 1,
  /** Shrink the rendered canvas width to the longest actual wrapped line.
   *  Default `true` (matches the `isCompressionProfitable` default and is
   *  correct for per-block content: tool_result, reminder, history). Set
   *  `false` for the system slab path, which fills the full configured
   *  `cols` deliberately for multi-col packing. */
  shrinkWidth: boolean = true,
): Promise<{
  blocks: ImageBlock[];
  droppedChars: number;
  droppedCodepoints: Map<number, number>;
  /** Total pixel area across the rendered images (`Σ width × height`).
   *  Lets the caller accumulate `info.imagePixels` for the empirical
   *  px/token regression. */
  pixels: number;
}> {
  // Width-shrink at the renderer entry so the renderer's canvas matches
[assistant]
Reviewed src/core/proxy.ts.
[user]
Priya Moreau (the patch author) thinks jotai would be fine here, docs are nice.
[assistant]
jotai is a reasonable candidate; let me also benchmark nanostores.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
: Math.round(actual),
      saved_input_tokens: Math.round(saved),
      // saved_pct kept for back-compat with existing dashboard HTML; it is
      // the input-only number. New code should read saved_pct_input_only.
      saved_pct: round1(pctInput),
      saved_pct_input_only: round1(pctInput),
      saved_pct_of_total_bill: round1(pctTotal),
      // Honest "share of total bill saved" — measured-rows numerator over
      // ALL paid requests in the denominator (compressed + passthrough +
      // probe-failed). This is the number users actually want when they
      // ask "is pxpipe helping". Negative when flap-pollution from
      // passthrough turns exceeds the collapse win on measured turns.
      saved_pct_of_all_spend: round1(pctAllSpend),
      all_baseline_equivalent_weighted: Math.round(allBaselineEquiv),
      all_actual_input_weighted: Math.round(allActual),
      all_output_weighted: Math.round(allOutput),
      all_usage_requests: this.totals.allUsageRequests,
      // Direct observed split — replaces "share of spend saved" as the
      // headline. Total actual $ and average $/req per path, plus a delta
      // gated on `split_sufficient_sample`. No counterfactual: each
      // bucket is what each path actually billed.
      compressed_paid_requests: this.totals.compressedPaidRequests,
      passthrough_paid_requests: this.totals.passthroughPaidRequests,
      compressed_actual_usd: round4(compressedActualUsd),
      passthrough_actual_usd: round4(passthroughActualUsd),
      compressed_avg_usd_per_request: round4(compressedAvgUsd),
      passthrough_avg_usd_per_request: round4(passthroughAvgUsd),
      compressed_minus_passthrough_avg_usd: round4(splitDeltaUsd),
      split_sufficient_sample: splitSufficient,
      split_min_sample_per_bucket: SUFFICIENT,
      saved_usd: round4((saved * ASSUMED_INPUT_USD_PER_MTOK) / 1e6),
      output_weighted: Math.round(output),
      baseline_token_equivalent: Math.round(baselineTotal),
      actual_token_equivalent: Math.round(actualTotal),
      pricing_assumptions: {
        input_per_mtok: ASSUMED_INPUT_USD_PER_MTOK,
        output_multiplier: OUTPUT_TOKEN_RATE,
        cache_write_5m_multiplier: 1.25,
        cache_write_1h_multiplier: 2.0,
        cache_read_multiplier: 0.1,
        source: 'docs.anthropic.com/en/docs/about-claude/pricing (verified 2026-05-19)',
      },
      // Honest output measurement — char counts from the SSE/JSON scanner,
      // independent of Anthropic's `usage.output_tokens`. Surfaces the gap
      // the May-2026 weekly-meter audit hypothesized (redacted_thinking adds
      // billed tokens that we can't see). `events_with_measurement` lets the
      // operator weigh how representative the numbers are; when it's near
      // `requests`, the gap is real. When it's 0, the scanner never landed
      // (5xx-heavy session, no /v1/messages traffic).
      measured_text_chars: this.totals.textCharsMeasured,
      measured_thinking_chars: this.totals.thinkingCharsMeasured,
      measured_tool_use_chars: this.totals.toolUseCharsMeasured,
      measured_redacted_block_count: this.totals.redactedBlockCountMeasured,
      events_with_measurement: this.totals.eventsWithMeasurement,
      uptime_sec: uptimeSec,
      compression_enabled: this.compressionEnabled,
    };
    return new Response(JSON.stringify(payload, null, 2), {
      headers: { 'content-type': 'application/json', 'access-co
[assistant]
Reviewed src/core/transform.ts.
[assistant]
Note: the cache TTL is 9350ms, unrelated to the retry budget discussion.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
osition we covered).
    let n = 0;
    for (let i = 0; i < fitLines.length; i++) {
      for (const _ of fitLines[i]!) n++;
    }
    // Each pair of adjacent fitLines was separated by either an input '\n'
    // or a soft-wrap point; we cover (fitLines.length - 1) such separators.
    n += Math.max(0, fitLines.length - 1);
    charsRendered = n;
  }

  // When cellW < the glyph width, the last glyph overruns its cell; widen the
  // canvas by that overhang so it stays inside the framebuffer.
  const width = 2 * PAD_X + cols * cellW + Math.max(0, atlasW - cellW);
  const height = 2 * PAD_Y + fitLines.length * cellH;

  // Black canvas (matches atlas: text is white-on-black, we invert below to
  // black-on-white for crispness — same convention as the Python proxy).
  const fb = new Uint8Array(width * height);
  // Marker mask: 1 where a ↵ glyph was inked, so the red-output path can
  // recolor exactly those pixels. null when no red marker was requested.
  const markerMask: Uint8Array | null =
    style.markerRed ? new Uint8Array(width * height) : null;
  // Color-cycle mask: stores colorIndex+1 per inked pixel (0 = background).
  // Each successive glyph cell gets a different palette color so the vision
  // encoder sees a hard color boundary at every character boundary.
  const useColorCycle = style.colorCycle === true;
  const colorMask: Uint8Array | null =
    useColorCycle ? new Uint8Array(width * height) : null;

  let droppedChars = 0;
  const droppedCodepoints = new Map<number, number>();
  let glyphIndex = 0; // increments for every glyph cell (including spaces/missing)
  for (let row = 0; row < fitLines.length; row++) {
    const line = fitLines[row]!;
    const baseY = PAD_Y + row * cellH;
    let col = 0;
    for (const ch of line) {
      if (col >= cols) break; // shouldn't happen — wrap should have prevented
      const codepoint = ch.codePointAt(0)!;
      const baseX = PAD_X + col * cellW;
      const isMarker = codepoint === NL_SENTINEL_CP;
      // For colorCycle: determine palette color for this glyph cell.
      const colorIdx = glyphIndex % GLYPH_PALETTE.length;
      // colorSlot is colorIdx+1 (0 is reserved for background in colorMask).
      const colorSlot = colorIdx + 1;
      let advance: number;
      if (isMarker && markerScale > 1) {
        // Enlarged ↵: scaled horizontally only — a packed grid has no
        // vertical room, so a uniform scale-up would corrupt the next row.
        advance = blitGlyphScaled(fb, markerMask, width, height, baseX, baseY, codepoint, markerScale);
        // Also stamp colorMask for the enlarged marker pixels if colorCycle.
        if (colorMask) {
          for (let gy = 0; gy < atlasH; gy++) {
            const py = baseY + gy;
            if (py >= height) break;
            for (let gx = 0; gx < advance * cellW; gx++) {
              const px = baseX + gx;
              if (px >= width) break;
              const idx = py * width + px;
              if (fb[idx]! > 0) colorMask[idx] = colorSlot;
            }
          }
        }
      } else if (useAA) {
        advance = blitGlyphGray(fb, width, baseX, baseY, codepoint);
        // For AA + colorCycle: stamp colorMask for every pixel blitGlyphGray
        // wrote coverage into. We detect coverage by checking fb[idx] > 0
        // after the blit. Stamp the glyph's cell region.
        if (colorMask && advance > 0) {
          const srcW = advance * atlasW;
          for (let gy = 0; gy < atlasH; gy++) {
            const py = base
[assistant]
Reviewed src/core/transform.ts.
[assistant]
The symptom first appeared in src/mailbox/io.ts (stack trace top frame), still tracing root cause.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
       method: req.method,
        headers: outHeaders,
        body: bodyOut,
        // duplex is required by spec when sending a stream as body
        ...(bodyOut instanceof ReadableStream ? { duplex: 'half' } : {}),
      } as RequestInit);
    } catch (e) {
      fire(502, info, `upstream_error: ${(e as Error).message}`);
      return new Response(JSON.stringify({ error: 'pxpipe upstream unreachable' }), {
        status: 502,
        headers: { 'content-type': 'application/json' },
      });
    }

    const firstByteMs = Date.now() - t0;

    // Tee the upstream body so we can extract Anthropic's usage block. The
    // client gets one side immediately; we read the other in the background.
    // For 4xx responses we also tee to capture the error body (up to 2 KiB)
    // so the host can log what Anthropic actually rejected.
    const { response: teed, usagePromise, errorBodyPromise, measurementPromise } =
      teeForUsage(upstreamRes);

    // Fire the host event once usage AND any captured error body AND the output
    // measurement are known (or once we've given up on finding them). Don't
    // await — the response below is what unblocks the client; fire happens in
    // the background. measurementPromise resolves from the same shared stream
    // read as usagePromise, so this Promise.all doesn't add latency.
    void Promise.all([
      usagePromise.catch(() => undefined),
      errorBodyPromise.catch(() => undefined),
      measurementPromise.catch(() => undefined),
    ]).then(([usage, errorBody, measurement]) =>
      fire(upstreamRes.status, info, undefined, firstByteMs, usage, errorBody, measurement),
    );

    return new Response(teed.body, {
      status: upstreamRes.status,
      statusText: upstreamRes.statusText,
      headers: filterHeaders(upstreamRes.headers, STRIP_RES_HEADERS),
    });
  };
}
/**
 * History-image compression (Variant C).
 *
 * Walks `messages[]` left-to-right tracking open `tool_use_id`s. Identifies
 * the largest **closed-tool-sequence prefix** — the longest run from the
 * head of the conversation that has no straddling `tool_use` references
 * into the live tail. Renders that prefix's text content into one or more
 * PNG image blocks and replaces the prefix with ONE synthetic user message:
 *
 *   { role: 'user', content: [
 *     { type: 'text', text: '[Earlier in this conversation:]' },
 *     { type: 'image', source: {...} },           // (1..N images)
 *     { type: 'text', text: '[End of earlier context.]' },
 *   ]}
 *
 * Live tail (the last `keepTail` turns + anything inside an open tool
 * sequence) stays as text. The most-recent assistant turn — the one
 * carrying Opus 4.7's `thinking` signature — is always in the live tail
 * by construction (it's at index `messages.length - 1` when present).
 *
 * The synthesized user message uses `role: 'user'` because Anthropic
 * **forbids `image` blocks inside `role: 'assistant'`** (see
 * `/tmp/pxpipe-history-compression.md` line 14 and `types.ts:58`
 * comments). Self-attribution ("I previously said X") is the price.
 *
 * `thinking` blocks inside the collapsed range are dropped from the
 * rendered text — per the spec's Check 2, only the most-recent
 * assistant-with-tool_use's thinking content must round-trip bit-perfect,
 * and that turn is in the live tail by construction.
 *
 * **Cache-control**: caller controls whether the history-image carries
 * pxpipe's ephemeral breakpoint. This module returns the image blocks
 *
[assistant]
Reviewed src/core/transform.ts.
[user]
staging note: LEGACY_PINS IS enabled in staging since Tuesday.
[assistant]
Ack, LEGACY_PINS on in staging.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
      // baselineInputEff / actualInputEff locals computed earlier in
      // update() so the lifetime totals block (above) and the per-session
      // block (here) read the same values. Re-deriving them here would
      // duplicate the cache-aware-baseline math and invite drift.
      if (haveBaseline && haveUsage) {
        s.baselineInputWeighted += baselineInputEff;
        s.actualInputWeighted += actualInputEff;
        s.baselineMeasuredCount += 1;
      }
      // ALL-rows session bill — mirrors the global `if (haveUsage)` block
      // above (allActualInputWeighted / allOutputWeighted). Used as the
      // honest denominator for the session's saved-% so caching wins on
      // unmeasured requests still count toward "what you actually paid".
      if (haveUsage) {
        s.allActualInputWeighted += actualInputEff;
        s.allOutputWeighted += outputEquiv;
      }
    }

    // Measurement totals are independent of usage/baseline gating — they
    // accumulate whenever the scanner produced numbers. The scanner sets
    // measurement to undefined on 5xx (no body to scan) and on unknown
    // content-types; we count an event as "measured" when it has any.
    const m = ev.measurement;
    if (m) {
      this.totals.textCharsMeasured += m.textChars;
      this.totals.thinkingCharsMeasured += m.thinkingChars;
      this.totals.toolUseCharsMeasured += m.toolUseChars;
      this.totals.redactedBlockCountMeasured += m.redactedBlockCount;
      this.totals.eventsWithMeasurement += 1;
    }

    const row: RecentRow = {
      ts: Date.now() / 1000,
      method: ev.method,
      path: ev.path,
      status: ev.status,
      compressed,
      cc_added: compressed ? 1 : undefined,
      input_tokens: haveUsage ? inp : undefined,
      output_tokens: haveUsage ? out : undefined,
      cache_create: haveUsage ? cc : undefined,
      cache_read: haveUsage ? cr : undefined,
      actual_input: haveUsage ? round1(actualInputEff) : undefined,
      baseline_input: haveBaseline && haveUsage ? round1(baselineInputEff) : undefined,
      session_saved_so_far_delta:
        haveBaseline && haveUsage ? round1(baselineInputEff - actualInputEff) : undefined,
      img_id: imgId,
      img_ids: imgIds,
    };
    this.recent.push(row);
    if (this.recent.length > RECENT_CAP) this.recent.splice(0, this.recent.length - RECENT_CAP);
  }


  /** On startup, fold the last N entries from the JSONL events file back
   *  into the ring buffer so a process restart doesn't show an empty table.
   *  Cumulative totals are *not* restored (the file may have rotated, and
   *  double-counting is worse than starting fresh). */
  async replay(filePath: string): Promise<void> {
    try {
      await fs.promises.access(filePath, fs.constants.R_OK);
    } catch {
      return; // no file yet, nothing to replay
    }
    const stream = fs.createReadStream(filePath, { encoding: 'utf8' });
    const rl = readline.createInterface({ input: stream, crlfDelay: Infinity });
    const tail: TrackEvent[] = [];
    for await (const line of rl) {
      if (!line) continue;
      try {
        const ev = JSON.parse(line) as TrackEvent;
        tail.push(ev);
        if (tail.length > RECENT_CAP) tail.shift();
      } catch {
        /* skip malformed line */
      }
    }
    for (const t of tail) {
      const inp = t.input_tokens ?? 0;
      const out = t.output_tokens ?? 0;
      const cc = t.cache_create_tokens ?? 0;
      const cr = t.cache_read_tokens ?? 0;
      const haveUsage = inp > 0 || out > 0 || cc > 0 || cr > 0;
      const baseline = (t as { baseline_tokens?: number }).baseline_tokens;
      const cacheable = (t as { baseline_cacheable_tokens?: number })
        .baseline_cacheable_tokens ?? 0;
      const probeStatus = (t as { baseline_probe_status?: string }).baseline_probe_status;
      // Same gating rule as update(): require an explicit 'ok' status when
      // present; fall back to "have a baseline number" for legacy JSONL.
      const probeOk = probeStatus === 'ok'
        || (probeStatus === undefined && typeof baseline === 'number' && baseline > 0);
      const haveBaseline = typeof baseline === 'number' && baseline > 0 && probeOk;
      const actualInputEff = haveUsage ? computeActualInputEff(inp, cc, cr) : 0;
      const baselineInputEff =
        haveBaseline && haveUsage
          ? computeBaselineInputEff(baseli
[assistant]
Reviewed src/core/render.ts.
[user]
final call after benchmarks: store layer goes with nanostores; jotai rejected, bundle delta too big.
[assistant]
Locked in: nanostores.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
o the dashboard's "current session" panel can show what's happening
    // RIGHT NOW instead of stale lifetime numbers. Untagged events (no
    // firstUserSha8 — cold start, passthrough probe failures) are skipped
    // rather than bucketed into a synthetic "unknown" session.
    const sid = info?.firstUserSha8;
    if (typeof sid === 'string' && sid.length > 0) {
      this.currentSessionId = sid;
      let s = this.sessions.get(sid);
      if (!s) {
        s = {
          sessionId: sid,
          baselineInputWeighted: 0,
          actualInputWeighted: 0,
          baselineMeasuredCount: 0,
          allActualInputWeighted: 0,
          allOutputWeighted: 0,
        };
        this.sessions.set(sid, s);
        // Cap memory — drop the first (oldest by insertion order) session
        // when over budget. We no longer track lastSeen privately on the
        // class — insertion order is a fine proxy because `currentSessionId`
        // (set above on every update) is what the serve path uses to pick
        // the most-recent session, not a scan of `this.sessions`.
        if (this.sessions.size > DashboardState.SESSION_CAP) {
          const firstKey = this.sessions.keys().next().value;
          if (firstKey !== undefined) this.sessions.delete(firstKey);
        }
      }
      // Reuse the same haveUsage / haveBaseline guards + the
      // baselineInputEff / actualInputEff locals computed earlier in
      // update() so the lifetime totals block (above) and the per-session
      // block (here) read the same values. Re-deriving them here would
      // duplicate the cache-aware-baseline math and invite drift.
      if (haveBaseline && haveUsage) {
        s.baselineInputWeighted += baselineInputEff;
        s.actualInputWeighted += actualInputEff;
        s.baselineMeasuredCount += 1;
      }
      // ALL-rows session bill — mirrors the global `if (haveUsage)` block
      // above (allActualInputWeighted / allOutputWeighted). Used as the
      // honest denominator for the session's saved-% so caching wins on
      // unmeasured requests still count toward "what you actually paid".
      if (haveUsage) {
        s.allActualInputWeighted += actualInputEff;
        s.allOutputWeighted += outputEquiv;
      }
    }

    // Measurement totals are independent of usage/baseline gating — they
    // accumulate whenever the scanner produced numbers. The scanner sets
    // measurement to undefined on 5xx (no body to scan) and on unknown
    // content-types; we count an event as "measured" when it has any.
    const m = ev.measurement;
    if (m) {
      this.totals.textCharsMeasured += m.textChars;
      this.totals.thinkingCharsMeasured += m.thinkingChars;
      this.totals.toolUseCharsMeasured += m.toolUseChars;
      this.totals.redactedBlockCountMeasured += m.redactedBlockCount;
      this.totals.eventsWithMeasurement += 1;
    }

    const row: RecentRow = {
      ts: Date.now() / 1000,
      method: ev.method,
      path: ev.path,
      status: ev.status,
      compressed,
      cc_added: compressed ? 1 : undefined,
      input_tokens: haveUsage ? inp : undefined,
      output_tokens: haveUsage ? out : undefined,
      cache_create: haveUsage ? cc : undefined,
      cache_read: haveUsage ? cr : undefined,
      actual_input: haveUsage ? round1(actualInputEff) : undefined,
      baseline_input: haveBaseline && haveUsage ? round1(baselineInputEff) : undefined,
      session_saved_so_far_delta:
        haveBaseline && haveUsage ? round1(baselineInputEff - actualInputEff) : undefined,
      img_id: imgId,
      img_ids: imgIds,
    };
    this.recent.push(row);
    if (this.recent.length > RECENT_CAP) this.recent.splice(0, this.recent.length - RECENT_CAP);
  }


  /** On startup, fold the last N entries from the JSONL events file back
   *  into the ring buffer so a process restart doesn't show an empty table.
   *  Cumulative totals are *not* restored (the file may have rotated, and
   *  double-counting is worse than starting fresh). */
  async replay(filePath: string): Promise<void> {
    try {
      await fs.promises.access(filePath, fs.constants.R_OK);
    } catch {
      return; // no file yet, nothing to replay
    }
    const stream = fs.createReadStream(filePath, { encoding: 'utf8' });
    const rl = readline.createInterface({ input: stream, crlfDelay: Infinity }
[assistant]
Reviewed src/core/proxy.ts.
[user]
ops: retry budget is exactly 7850ms, do not confuse it with the cache TTL.
[assistant]
Retry budget set: 7850ms.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
). */
    readonly textTokens: number;
    /** `priorWarmTokens × (1.25 − 0.10)` applied to the image side. */
    readonly burnImageSide: number;
    /** `priorWarmImageTokens × (1.25 − 0.10)` applied to the text side.
     *  Non-zero rows are the anti-flapping anchor — text would otherwise
     *  have looked cheaper. */
    readonly burnTextSide: number;
    /** Gate's verdict; `true` ⇒ compression applied on this turn. */
    readonly profitable: boolean;
  };
  /** Per-bucket sum of TEXT chars that flowed through each gate-call site
   *  (static slab, reminder, tool_result by classifyContent shape, history).
   *  Pre-compaction lengths — stays comparable to `origChars` and to what
   *  Anthropic would have billed if compression were off. Used by the
   *  rolling-cpt regression (Task #18) to learn per-bucket marginal cpts
   *  from production telemetry instead of relying on one global constant.
   *  Absent when no bucket fired this request. */
  bucketChars?: BucketChars;
  /** Variant C history bucket: chars of TEXT that fed into the history-image
   *  renderer (post-`messagesToHistoryText`, pre-`renderTextToPngs`). Folded
   *  into `bucketChars.history` too — surfaced separately so the regression
   *  can credit history-image cost even on no-collapse paths (where the
   *  collapsed-prefix gate ran but landed on `not_profitable` / `render_empty`
   *  and we still want to record that the bucket saw text). */
  historyTextChars?: number;
  /** Number of tool_result blocks where the source text exceeded the
   *  per-tool_result image budget and was truncated before rendering. */
  truncatedToolResults?: number;
  /** Total chars elided by paging across all tool_results this request. */
  omittedChars?: number;
  /** Variant C history-image: how many original `messages[]` entries got
   *  collapsed into the prepended synthetic user message. 0 / unset when
   *  no collapse happened (no closed prefix, too few turns, gate rejected
   *  as not_profitable, etc. — see `historyReason`). */
  collapsedTurns?: number;
  /** Variant C: total chars of text serialized into the history image(s)
   *  before render (pre-OCR loss). */
  collapsedChars?: number;
  /** Variant C: number of PNG image blocks emitted for the history. Folded
   *  into `info.imageCount` too — surfaced separately so dashboards can
   *  attribute image-count growth to history vs system-slab vs reminders. */
  collapsedImages?: number;
  /** Variant C: sha8 of the concatenated history-image base64 emitted this
   *  request. The quantized collapse boundary keeps the synthetic history
   *  message byte-identical for a full `collapseChunk` window — an UNCHANGED
   *  `history_image_sha8` across consecutive collapsed events is the
   *  ground-truth proof that the upstream prompt cache can `cache_read` the
   *  history prefix (0.1x) instead of re-billing `cache_create` (1.25x). A
   *  hash that changes every turn ⟹ the cache-key drift bug is back. Only
   *  set when a collapse actually produced image blocks. */
  historyImageSha?: string;
  /** Variant C: why the history collapse didn't run (or did). Diagnostic
   *  only — see `HistoryCollapseInfo.reason` for the value set. */
  historyReason?:
    | 'no_history'
    | 'prefix_too_short'
    | 'no_closed_prefix'
    | 'not_profitable'
    | 'render_empty'
    | 'collapsed';
  /** Ground-truth baseline token count for THIS request, from a parallel
   *  call to /v1/messages/count_tokens on the PRE-COMPRESSION body. The
   *  endpoint is free (no input-token billing). Absent when the probe
   *  failed (network, 4xx) — that event is then excluded from the
   *  savings rollup. */
  baselineTokens?: number;
  /** Second baseline probe: input_tokens of the original body TRUNCATED at
   *  the last `cache_control` marker — the prefix that would have cached
   *  on the unproxied path. Used by the dashboard to weight the baseline by
   *  the SAME cache class the proxied request landed in (cache_create ×1.25,
   *  cache_read ×0.10, no-cache ×1.0), giving an exact cache-aware
   *  counterfactual instead of cold-every-time. Absent when the original
   *  body has no cache_control markers anywhere (in which case the unproxied
   *  path doesn't cache and cacheable_prefix_tokens = 0). */
  baselineCacheableTokens?: number;
  /** Status of the cache-aware baseline probe for this
[assistant]
Reviewed src/core/proxy.ts.
[assistant]
Root cause found: the double-flush race is in src/mailbox/core.ts; src/mailbox/io.ts was only the symptom site.
[user]
fix only the root cause file.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
 ?? 0) + pixels;
                info.toolResultImgs = (info.toolResultImgs ?? 0) + imgs.length;
                info.imageCount += imgs.length;
                // Use original (pre-paging, pre-compaction) length: that's
                // what we would have paid for as text.
                info.compressedChars += innerRaw.length;
                info.droppedChars = (info.droppedChars ?? 0) + droppedChars;
                for (const [cp, n] of dcp) {
                  droppedCodepoints.set(cp, (droppedCodepoints.get(cp) ?? 0) + n);
                }
                rewritten.push({ ...tr, content: imgs });
                changed = true;
                // Phase 1 (Task #18): bucket tool_result text by content shape
                // so structured (JSON/YAML/diff), log, and prose can each track
                // their own marginal cpt. Use the post-compaction text since
                // that matches what the gate evaluated and what got imaged.
                bumpBucket(info, toolResultBucket(classifyContent(inner)), innerRaw.length);
              }
            } else if (Array.isArray(innerRaw)) {
              const newInner: Array<TextBlock | ImageBlock> = [];
              let innerChanged = false;
              for (const ib of innerRaw) {
                const isTextBlock =
                  ib &&
                  (ib as TextBlock).type === 'text' &&
                  typeof (ib as TextBlock).text === 'string';
                if (!isTextBlock) {
                  newInner.push(ib as TextBlock | ImageBlock);
                  continue;
                }
                const innerTextRaw = (ib as TextBlock).text;
                // Lossless whitespace compaction before gate + render.
                const innerText = compactSlabWhitespace(innerTextRaw);
                // R3: gate/page/render on reflowed text; classify pre-reflow.
                const innerTextR = maybeReflow(innerText, o.reflow);
                if (innerTextR.length < o.minToolResultChars) {
                  bumpPassthrough(info, 'below_threshold');
                  newInner.push(ib as TextBlock | ImageBlock);
                  continue;
                }
                if (!isCompressionProfitable(innerTextR, o.cols, o.maxImagesPerToolResult, numCols, o.charsPerToken)) {
                  bumpPassthrough(info, 'not_profitable');
                  newInner.push(ib as TextBlock | ImageBlock);
                  continue;
                }
                const paged = truncateForBudget(innerTextR, o.maxImagesPerToolResult, o.cols, numCols);
                if (paged.truncated) {
                  info.truncatedToolResults = (info.truncatedToolResults ?? 0) + 1;
                  info.omittedChars = (info.omittedChars ?? 0) + paged.omittedChars;
                }
                const { blocks: imgs, droppedChars, droppedCodepoints: dcp, pixels } =
                  await textToImageBlocks(paged.text, o.cols, numCols);
                // Preserve any cache_control the caller set on this inner
                // text block (inside a tool_result) by re-attaching it to the
                // LAST produced image. pxpipe never adds new markers (Task #21).
                const srcCacheControl = (ib as { cache_control?: unknown }).cache_control;
                for (let i = 0; i < imgs.length; i++) {
                  const img = imgs[i]!;
                  const out =
                    i === imgs.length - 1 && srcCacheControl !== undefined
                      ? { ...img, cache_control: srcCacheControl }
                      : img;
                  newInner.push(out as ImageBlock);
                  info.imageBytes += approxBlockBytes(img);
                }
                info.imagePixels = (info.imagePixels ?? 0) + pixels;
                info.toolResultImgs = (info.toolResultImgs ?? 0) + imgs.length;
                info.imageCount += imgs.length;
                // Credit raw length — billed equivalent if compression were off.
                info.compressedChars += innerTextRaw.length;
                info.droppedChars = (info.droppedChars ?? 0) + droppedChars;
                for (const [cp, n] of dcp) {
                  droppedCodepoints.set(cp, (droppedCodepoints.get(cp) ?? 0) + n);
                }
                // Phase 1 (Task #18): per-block bucket attributio
[assistant]
Reviewed src/core/proxy.ts.
[user]
routing: the on-call REVIEWER is Aiko Khoury; Priya Moreau stays author and cannot self-review.
[assistant]
PR review to Aiko Khoury.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
pSchemaDescriptions(v, depth + 1);
      }
      continue;
    }

    // Unknown key. If the value is a nested object, recurse so descriptions
    // hidden under vendor extensions still get stripped. Primitives pass
    // through.
    if (v && typeof v === 'object') {
      out[k] = stripSchemaDescriptions(v, depth + 1);
    } else {
      out[k] = v;
    }
  }
  return out;
}

/** Keys whose presence in a (stripped) schema gives Anthropic's validator
 *  something to bind the model's tool call against. If a stripped schema has
 *  *none* of these, we treat it as no-structure and ship the legacy bare stub
 *  with a `schema_no_properties` advisory. */
const SCHEMA_STRUCTURAL_KEYS = [
  'properties',
  'patternProperties',
  'oneOf',
  'anyOf',
  'allOf',
  'items',
  '$ref',
  'enum',
  'const',
];

function schemaHasStructure(schema: Record<string, unknown>): boolean {
  for (const k of SCHEMA_STRUCTURAL_KEYS) {
    if (k in schema) return true;
  }
  return false;
}

/** Build the "## Tool: name\n<desc>\n<schema>" block for one tool definition.
 *
 *  Schema serialization is **compact** (no whitespace). Pretty-printing
 *  with 2-space indent was the dominant source of sparse fill: each schema
 *  key on its own line, indented, wastes 70%+ of horizontal space at
 *  cols=100. Live measurement on 2026-05-19 showed 150 KB of pretty
 *  tool-doc JSON across ~30 tools rendering to 31 static-slab images per
 *  request — a 40% fill ratio that pushed every request well past the
 *  break-even point.
 *
 *  Compact form is still unambiguous JSON. Descriptions are already
 *  stripped under compressSchemas so only structural keys
 *  (type/properties/required/enum/items) remain — they read fluently
 *  on one line. Frontier models handle compact JSON natively (it's the
 *  default wire format for tool_use blocks). */
function renderToolDoc(t: ToolDef, includeSchema: boolean): string {
  const parts: string[] = [`## Tool: ${t.name ?? '?'}`];
  if (t.description) parts.push(t.description);
  if (includeSchema && t.input_schema !== undefined) {
    parts.push('```json\n' + JSON.stringify(t.input_schema) + '\n```');
  }
  return parts.join('\n');
}

function makeImageBlock(pngB64: string, _ephemeral = false): ImageBlock {
  // Per Task #21: pxpipe NEVER adds its own cache_control marker.
  // Claude Code already places markers on system+tools, CLAUDE.md, and the
  // per-turn anchor; we honor those positions byte-identically and add
  // nothing of our own. The `_ephemeral` parameter is preserved for call-
  // site compatibility but is now a no-op.
  return {
    type: 'image',
    source: { type: 'base64', media_type: 'image/png', data: pngB64 },
  };
}

/** Render a long text blob to one or more PNG image blocks. Helper for the
 *  per-message compressions (reminders, tool_results) — no cache_control on
 *  these (Anthropic caps at 4 breakpoints; the system+tools image already
 *  anchors the cacheable prefix).
 *
 *  Also returns the total `droppedChars` across all rendered images plus the
 *  merged codepoint→count map so the caller can fold both into the request's
 *  `info.droppedChars` / `info.droppedCodepointsTop`. */

// --- paging / truncation -------------------------------------------------
//
// Anthropic's API caps a request at 100 images. A single huge tool_result
// (find over a big tree, multi-MB log dump) can blow that cap by itself.
// To keep the request valid AND not waste tokens on dozens of bottom-of-log
// images, we truncate the source text before render with a marker that
// tells the model what was elided.

/** Visual rows a single input line will consume after soft-wrap at `cols`. */
function lineRows(line: string, cols: number): number {
  return Math.max(1, Math.ceil(line.length / cols));
}

/** Count the visual rows `text` will consume after soft-wrap at `cols`.
 *  Wrap-the-line reflow breaks the render row at every ↵, so both `\n` and
 *  the ↵ sentinel end a counted line — and the ↵ glyph occupies a cell on
 *  the line it terminates. */
function countVisualRows(text: string, cols: number): number {
  let rows = 0;
  let lineStart = 0;
  const len = text.length;
  for (let i = 0; i <= len; i++) {
    const cc = i < len ? text.charCodeAt(i) : -1;
    const isSentinel = cc === 0x21b5 /* ↵ */;
    if (i === len || cc === 10 /* \n */ || isSentinel) {
      
[assistant]
Reviewed src/core/transform.ts.
[user]
important: in PROD, LEGACY_PINS was NOT enabled, prod dashboard showed stale config cache.
[assistant]
Confirmed: LEGACY_PINS OFF in prod, ON only in staging.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
 no benefit.
 */
export function blocksToText(content: string | ContentBlock[]): string {
  if (typeof content === 'string') return content;
  const parts: string[] = [];
  for (const blk of content) {
    if (!blk || typeof blk !== 'object') continue;
    const t = (blk as { type?: string }).type;
    switch (t) {
      case 'text':
        parts.push((blk as TextBlock).text);
        break;
      case 'tool_use': {
        const tu = blk as ToolUseBlock;
        // Render as a labelled block so the model can re-attribute. Args
        // are serialised COMPACT (no 2-space indent) — pretty-printing
        // bloats the history text ~5× via per-field newlines, which
        // multiplies image cost since the renderer is row-aware and
        // every JSON field gets its own row. Compact JSON wraps at
        // `cols` like normal text, packing ~15.6k chars per single-col
        // image at the 7×10 cell instead of one short line per field.
        let argsStr: string;
        try {
          argsStr = JSON.stringify(tu.input);
        } catch {
          argsStr = String(tu.input);
        }
        parts.push(`[tool_use ${tu.name}]\n${argsStr}`);
        break;
      }
      case 'tool_result': {
        const tr = blk as ToolResultBlock;
        const inner = tr.content;
        let innerText: string;
        if (typeof inner === 'string') {
          innerText = inner;
        } else if (Array.isArray(inner)) {
          const subParts: string[] = [];
          for (const sub of inner) {
            if (!sub || typeof sub !== 'object') continue;
            if ((sub as TextBlock).type === 'text') {
              subParts.push((sub as TextBlock).text);
            } else if ((sub as ImageBlock).type === 'image') {
              subParts.push('[image]');
            }
          }
          innerText = subParts.join('\n');
        } else {
          innerText = '';
        }
        const errMark = tr.is_error === true ? ' (error)' : '';
        parts.push(`[tool_result${errMark}]\n${innerText}`);
        break;
      }
      case 'image':
        parts.push('[image]');
        break;
      // 'thinking' and any other block type → drop silently.
      default:
        break;
    }
  }
  return parts.join('\n\n');
}

/**
 * Serialize messages `[0..upToExclusive]` to a single OCR-friendly text
 * blob. Each turn is prefixed with `--- role ---` so the model can parse
 * the conversation back out. Empty turns are skipped.
 */
export function messagesToHistoryText(
  messages: Message[],
  upToExclusive: number,
): string {
  const out: string[] = [];
  for (let i = 0; i < upToExclusive; i++) {
    const m = messages[i]!;
    const body = blocksToText(m.content);
    if (!body.trim()) continue;
    const tag = m.role === 'assistant' ? 'assistant' : 'user';
    out.push(`--- ${tag} ---\n${body}`);
  }
  return out.join('\n\n');
}

/**
 * Attempt to collapse a closed-prefix run of `messages` into one synthetic
 * user message containing 1+ history images. Returns the rewritten
 * messages array (a new array; original is not mutated) and telemetry.
 *
 * On any "do not collapse" path (no prefix, too few turns, not profitable,
 * empty render), returns the original messages unchanged with a reason.
 *
 * Caller is responsible for cache_control placement on the returned image
 * blocks — this function returns them with NO `cache_control` set.
 */
export async function collapseHistory(
  messages: Message[],
  isProfitable: ProfitableFn,
  opts: Partial<HistoryCollapseOptions> = {},
): Promise<{ messages: Message[]; info: HistoryCollapseInfo }> {
  const o: HistoryCollapseOptions = { ...HISTORY_DEFAULTS, ...opts };
  const info: HistoryCollapseInfo = {
    collapsedTurns: 0,
    collapsedChars: 0,
    collapsedImages: 0,
    collapsedImageBytes: 0,
    collapsedImagePixels: 0,
    droppedChars: 0,
    droppedCodepoints: new Map(),
  };
  if (!messages || messages.length === 0) {
    info.reason = 'no_history';
    return { messages: messages ?? [], info };
  }
  // The live tail must contain at least `keepTail` messages. The boundary
  // search cuts off at `len - keepTail` so the tail is always preserved.
  //
  // Quantize that cutoff onto a fixed grid of `collapseChunk` messages.
  // A moving boundary re-renders the history image — and changes its PNG
  // bytes — on every turn, which misses Anthropic's prompt cache and
  // forces a full `cache_create` (1.25x) of the whole prefix every turn.
  // Snapping to a grid keeps the collapsed prefix — and thus the rendered
  // image — byte-identical for `collapseChunk` turns at a stretch, so the
  // history image caches like Claude Code's native byte-stable history.
  const rawCutoff = messages.length - o.keepTail;
  // Snap the cutoff to the grid, but never below `minCollapsePrefix`. A
  // conversation shorter than one full `collapseChunk` would otherwise
  // floor straight to 0 and skip history compression entirely. Flooring
  // at `minCollapsePrefix` instead keeps the boundary — and therefore the
  // rendered image — byte-stable (the prefix is append-only, so its first
  // `minCollapsePrefix` messages never change) while still collapsing
  // short histories. Clamp to `rawCutoff` so a floor can never reach past
  // the live tail when `rawCutoff < minCollapsePrefix`.
  const cutoff =
    o.collapseChunk > 0
      ? Math.min(
          rawCutoff,
          Math.max(
            o.minCollapsePrefix,
            Math.floor(rawCutoff / o.collapseChunk) * o.collapseChunk,
          ),
        )
      : rawCutoff;
  const boundary = findClosedPrefixBoundary(messages, cutoff);
  if (boundary < 0) {
    info.reason = 'no_closed_prefix';
    return { messages, info };
  }
  // boundary is the last index INCLUDED in the collapse. Need at least
  // `minCollapsePrefix` turns to bother (cache-amortization math from
  // round-3 only works at scale; collapsing 2-3 turns is net cost).
  const collapseLen = boundary + 1;
  if (collapseLen < o.minCollapsePrefix) {
    info.reason = 'prefix_too_short';
    return { messages, info };
  }
  // Serialize and gate on break-even.
  const text = messagesToHistoryText(messages, collapseLen);
  if (!text || text.length === 0) {
    info.reason = 'render_empty';
    return { messages, info };
  }
  // Row-aware: pass the string, not its length. See ProfitableFn jsdoc.
  if (!isProfitable(text, o.cols)) {
    info.reason = 'not_profitable';
    info.collapsedChars = text.length; // surface what we DIDN'T compress
    return { messages, info };
  }
  // Render. No cache_control here — caller decides placement.
  // Dense history is user-visible context, not the static system-slab cache
  // anchor. Render it with the readable dense profile instead of the 313-col
  // full-canvas profile; otherwise lockfiles/code/config collapse into pixel mush.
  const imgs = await renderTextToPngsWithCharLimit(text, DENSE_CONTENT_COLS, DENSE_CONTENT_CHARS_PER_IMAGE, DENSE_RENDER_STYLE);
  if (imgs.length === 0) {
    info.reason = 'render_empty';
    return { messages, info };
  }
  const imageBlocks: ImageBlock[] = [];
  for (const img of imgs) {
    imageBlocks.push({
      type: 'image',
      source: {
        type: 'base64',
        media_type: 'image/png',
        data: bytesToBase64(img.png),
      },
    });
    info.collapsedImageBytes += img.png.length;
    info.collapsedImagePixels += img.width * img.height;
    info.droppedChars += img.droppedChars;
    for (const [cp, n] of img.droppedCodepoints) {
      info.droppedCodepoints.set(cp, (info.droppedCodepoints.get(cp) ?? 0) + n);
    }
  }
  // Build the synthetic user message.
  const syntheticContent: ContentBlock[] = [
    { type: 'text', text: '[Earlier in this conversation:]' },
    ...imageBlocks,
    { type: 'text', text: '[End of earlier context.]' },
  ];
  const syntheticUser: Message = {
    role: 'user',
    content: syntheticContent,
  };
  const tail = messages.slice(collapseLen);
  info.collapsedTurns = collapseLen;
  info.collapsedChars = text.length;
  info.collapsedImages = imageBlocks.length;
  return { messages: [syntheticUser, ...tail], info };
}
/**
 * Live dashboard for the Node host. Serves the main HTML page and JSON
 * polling endpoints. All "/api/*.json" endpoints recompute from disk on
 * every request — pxpipe doesn't have a query layer, but a 1.5 MB JSONL
 * streams in well under 100 ms.
 *
 * Legacy live-poll endpoints (left in place, the existing tick() loop uses
 * them):
 *
 *   GET  /, /dashboard               → main HTML page
 *   GET  /proxy-stats                → JSON aggregate over the in-mem ring
 *   GET  /proxy-recent               → JSON ring buffer of recent requests
 *   GET  /proxy-latest-png[?crop=N]  → raw PNG of the latest rendered image
 *
 * Session endpoints (read-only telemetry — no destructive ope
[assistant]
Reviewed src/core/render.ts.

=== end ===
