=== session s4 transcript ===
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
pes> trigger the canary on most turns
 * and drown out the real signal. Add a tag here only after confirming it's
 * static (appears in the cacheable part of the prompt, not rotated per turn).
 */
const KNOWN_STATIC_TAGS = ['types'] as const;

function splitStaticDynamic(text: string): {
  staticText: string;
  dynamicText: string;
  blockCount: number;
  unknownTags: string[];
} {
  if (!text)
    return { staticText: '', dynamicText: '', blockCount: 0, unknownTags: [] };
  // Match <tag ...?>...</tag> where tag ∈ DYNAMIC_BLOCK_TAGS. Closing tag
  // must match opening tag exactly. Non-greedy body — earliest close wins.
  const pattern = new RegExp(
    `<(${DYNAMIC_BLOCK_TAGS.join('|')})(\\s[^>]*)?>[\\s\\S]*?</\\1>`,
    'g',
  );
  const dynamicParts: string[] = [];
  let staticBuf = '';
  let cursor = 0;
  let m: RegExpExecArray | null;
  while ((m = pattern.exec(text)) !== null) {
    staticBuf += text.slice(cursor, m.index);
    dynamicParts.push(m[0]);
    cursor = m.index + m[0].length;
  }
  staticBuf += text.slice(cursor);

  // Sniff for OTHER tag-shaped blocks in the static slab. If Claude Code
  // ships a new per-turn tag (say <recent_files>...</recent_files>) we'd
  // silently bake it into the cached image and our cache hit rate would
  // collapse. Surfacing the tag name as telemetry lets us detect that
  // within hours of a Claude Code release.
  const known = new Set<string>(DYNAMIC_BLOCK_TAGS);
  const knownStatic = new Set<string>(KNOWN_STATIC_TAGS);
  const sniffer = /<([a-zA-Z][a-zA-Z0-9_-]*)(?:\s[^>]*)?>[\s\S]*?<\/\1>/g;
  const unknown = new Set<string>();
  let s: RegExpExecArray | null;
  while ((s = sniffer.exec(staticBuf)) !== null) {
    const tag = s[1]!;
    if (!known.has(tag) && !knownStatic.has(tag) && tag.length <= 64)
      unknown.add(tag);
  }

  return {
    // Collapse the run of blank lines left behind by removed blocks.
    staticText: staticBuf.replace(/\n{3,}/g, '\n\n').trim(),
    dynamicText: dynamicParts.join('\n\n'),
    blockCount: dynamicParts.length,
    unknownTags: [...unknown],
  };
}

/**
 * Compute sha256 and return the first 8 hex chars. Web Crypto so it works
 * the same in Node 18+ and Workers. 8 chars = 32 bits = collision-safe for
 * the request volume we'd see in a single proxy instance.
 */
export async function sha8(text: string): Promise<string> {
  const buf = new TextEncoder().encode(text);
  const digest = await crypto.subtle.digest('SHA-256', buf);
  const bytes = new Uint8Array(digest);
  let hex = '';
  for (let i = 0; i < 4; i++) hex += bytes[i]!.toString(16).padStart(2, '0');
  return hex;
}

/**
 * Hash the concatenated base64 of every image block carried by the synthetic
 * hi
[assistant]
Reviewed src/core/proxy.ts.
[user]
Tobias Petrov (the patch author) thinks valtio would be fine here, docs are nice.
[assistant]
valtio is a reasonable candidate; let me also benchmark zustand.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
or (let gx = 0; gx < srcW; gx++) {
      const coverage = ATLAS_GRAY_PIXELS[srcRow + gx]!;
      if (coverage > 0) {
        const idx = dstRow + gx;
        if (coverage > fb[idx]!) fb[idx] = coverage;
      }
    }
  }
  return wide ? 2 : 1;
}

/** Blit a glyph scaled horizontally by `scaleX` (each atlas pixel becomes
 *  `scaleX` px wide; height unchanged). Used for the enlarged ↵ marker:
 *  horizontal-only scaling keeps it from overlapping the densely-packed row
 *  below, which a uniform scale-up would corrupt. Marks `markerMask` for the
 *  red-output path. Returns cells advanced (`scaleX`, `2*scaleX` if wide). */
function blitGlyphScaled(
  fb: Uint8Array,
  markerMask: Uint8Array | null,
  fbW: number,
  fbH: number,
  x: number,
  y: number,
  codepoint: number,
  scaleX: number,
): number {
  const rank = atlasRank(codepoint);
  if (rank < 0) return 0;
  const wide = ATLAS_WIDE_FLAGS[rank] === 1;
  const srcW = wide ? 2 * ATLAS_CELL_W : ATLAS_CELL_W;
  const srcOff = ATLAS_OFFSETS[rank]!;
  for (let gy = 0; gy < ATLAS_CELL_H; gy++) {
    const py = y + gy;
    if (py >= fbH) break;
    const bitRowStart = srcOff + gy * srcW;
    for (let gx = 0; gx < srcW; gx++) {
      const bitIdx = bitRowStart + gx;
      const byte = ATLAS_PIXELS[bitIdx >>> 3]!;
      if (((byte >>> (7 - (bitIdx & 7))) & 1) === 0) continue;
      for (let sx = 0; sx < scaleX; sx++) {
        const px = x + gx * scaleX + sx;
        if (px >= fbW) break;
        const idx = py * fbW + px;
        fb[idx] = 255;
        if (markerMask) markerMask[idx] = 1;
      }
    }
  }
  return wide ? 2 * scaleX : scaleX;
}

/** Faint grey grid ink, pre-invert. 25 → post-invert 230: a light-grey rule
 *  distinct from the multicol gutter divider (pre 64 → post 191) by both
 *  shade and orientation, so a row rule is never mistaken for a column edge. */
const GRID_INK = 25;

/** Paint grid rules into the framebuffer. Rules are written only onto
 *  background pixels — glyph ink always wins — so the grid adds zero pixels
 *  to the image (no width, no height, no token cost). It exists purely to
 *  give the vision model row/column landmarks that dense reflow packing
 *  destroys. Horizontal rule: bottom pixel-row of every cell-band (one ruled
 *  lane per text row). Vertical rules: every `gridCols` columns when > 0. */
function drawGrid(
  fb: Uint8Array,
  fbW: number,
  fbH: number,
  rows: number,
  gridCols: number,
  cellH: number,
  cellW: number,
  glyphH: number = ATLAS_CELL_H,
): void {
  for (let row = 0; row < rows; row++) {
    const y = PAD_Y + row * cellH + (glyphH - 1);
    if (y >= fbH) break;
    const rowStart = y * fbW;
    for (let x = 0; x < fbW; x++) {
      if (fb[rowStart + x] === 0) fb[rowStart + x] = GRID_INK;
    }
  }
  if (gridCols > 0) {
    for (let col = gridCols; ; col += gridCols) {
      const x = PAD_X + col * cellW;
      if (x >= fbW - PAD_X) break;
      for (let y = 0; y < fbH; y++) {
        const idx = y * fbW + x;
        if (fb[idx] === 0) fb[idx] = GRID_INK;
      }
    }
  }
}

/** Render up to `maxLines` of `text` to a single PNG, returning the unwritten
 *  tail. Each line gets one cell-row in the framebuffer; wide glyphs occupy
 *  two consecutive cells horizontally. */
export async function renderChunkToPng(
  text: string,
  cols: number = DEFAULT_COLS,
  style: RenderStyle = {},
): Promise<RenderedImage> {
  const useAA = style.aa === true;
  const atlasH
[assistant]
Reviewed src/core/transform.ts.
[assistant]
Note: the cache TTL is 11620ms, unrelated to the retry budget discussion.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
sion. */
  collapsedImagePixels: number;
  /** Why we didn't collapse — populated only when no collapse happened. */
  reason?:
    | 'no_history'
    | 'prefix_too_short'
    | 'no_closed_prefix'
    | 'not_profitable'
    | 'render_empty';
  /** Dropped codepoints from the history render, merged into the
   *  transform-wide map by the caller. */
  droppedChars: number;
  droppedCodepoints: Map<number, number>;
}


/**
 * Compute the largest index `i*` in `[0..messages.length - keepTail - 1]`
 * such that all `tool_use_id`s issued by assistant turns in `[0..i*]` are
 * matched by `tool_result`s also in `[0..i*]`. Returns `-1` if no such
 * boundary exists (i.e. every potential boundary has a tool_use straddling
 * into the live tail).
 *
 * Algorithm: walk left-to-right. Maintain an `openSet` of unmatched
 * tool_use_ids. After processing each message, record the current openSet
 * size. The closed-prefix boundary is the **last** index ≤ cutoff at which
 * openSet was empty AFTER processing.
 *
 * NOTE: this is robust to interleaved tool_use sequences (e.g. two parallel
 * tool calls in one assistant turn followed by two tool_results in the
 * next user turn). The openSet tracking handles that correctly.
 */
export function findClosedPrefixBoundary(
  messages: Message[],
  cutoffExclusive: number,
): number {
  if (cutoffExclusive <= 0) return -1;
  const openSet = new Set<string>();
  let lastClosed = -1;
  const limit = Math.min(cutoffExclusive, messages.length);
  for (let i = 0; i < limit; i++) {
    const msg = messages[i]!;
    if (!Array.isArray(msg.content)) {
      // Plain string content — no tool blocks possible. Just close-or-stay.
      if (openSet.size === 0) lastClosed = i;
      continue;
    }
    if (msg.role === 'assistant') {
      for (const blk of msg.content) {
        if (blk && (blk as ToolUseBlock).type === 'tool_use') {
          const id = (blk as ToolUseBlock).id;
          if (typeof id === 'string') openSet.add(id);
        }
      }
    } else if (msg.role === 'user') {
      for (const blk of msg.content) {
        if (blk && (blk as ToolResultBlock).type === 'tool_result') {
          const id = (blk as ToolResultBlock).tool_use_id;
          if (typeof id === 'string') openSet.delete(id);
        }
      }
    }
    if (openSet.size === 0) lastClosed = i;
  }
  return lastClosed;
}

/**
 * Linearise a content-block array to a single string for OCR. Drops
 * `thinking` blocks (Opus 4.7+ only requires bit-perfect on the most-recent
 * assistant-with-tool_use, which is in the live tail by construction).
 * Tool-use input args and tool-result content are included so the model
 * has full context. Inline images and tool_result images are reduced to a
 * `[image]` placeholder — embedding them in the history image would
 * double-encode for 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
        // multip
[assistant]
Reviewed src/core/proxy.ts.
[assistant]
The symptom first appeared in src/cursor/io.ts (stack trace top frame), still tracing root cause.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]

      }
    } else if (msg.role === 'user') {
      for (const blk of msg.content) {
        if (blk && (blk as ToolResultBlock).type === 'tool_result') {
          const id = (blk as ToolResultBlock).tool_use_id;
          if (typeof id === 'string') openSet.delete(id);
        }
      }
    }
    if (openSet.size === 0) lastClosed = i;
  }
  return lastClosed;
}

/**
 * Linearise a content-block array to a single string for OCR. Drops
 * `thinking` blocks (Opus 4.7+ only requires bit-perfect on the most-recent
 * assistant-with-tool_use, which is in the live tail by construction).
 * Tool-use input args and tool-result content are included so the model
 * has full context. Inline images and tool_result images are reduced to a
 * `[image]` placeholder — embedding them in the history image would
 * double-encode for 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[
[assistant]
Reviewed src/core/proxy.ts.
[user]
staging note: HOT_RELOAD_V2 IS enabled in staging since Tuesday.
[assistant]
Ack, HOT_RELOAD_V2 on in staging.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
Case())) out.append(k, v);
  });
  return out;
}

/** POST /v1/messages/count_tokens with the given body. Returns the upstream's
 *  `input_tokens` number or null on any failure. count_tokens is documented
 *  as a free endpoint (no input-token billing) — we use it once per request
 *  on the PRE-COMPRESSION body to get the ground-truth baseline. Actual
 *  post-compression tokens already come back free in the /v1/messages usage
 *  block (input_tokens + cache_create + cache_read), so no second probe. */
async function countTokensUpstream(
  upstream: string,
  body: Uint8Array,
  headers: Headers,
): Promise<number | null> {
  try {
    const res = await fetch(upstream + '/v1/messages/count_tokens', {
      method: 'POST',
      headers,
      body: body as unknown as BodyInit,
    });
    if (!res.ok) return null;
    const json = (await res.json()) as { input_tokens?: unknown };
    return typeof json.input_tokens === 'number' ? json.input_tokens : null;
  } catch {
    return null;
  }
}

/** Resolved upstream routing for a config. Pure — unit-testable.
 *  In gateway mode both API families ride one base URL on their own
 *  provider routes; OpenAI paths drop the `/v1` prefix to match the
 *  gateway's path shape. No protocol translation anywhere. */
export function resolveUpstreams(config: ProxyConfig): {
  anthropic: string;
  openai: string;
  stripOpenAIV1: boolean;
} {
  if (config.provider === 'cloudflare-ai-gateway') {
    const base = (config.gatewayBaseUrl ?? '').replace(/\/+$/, '');
    if (!base) {
      throw new Error(
        "provider 'cloudflare-ai-gateway' requires gatewayBaseUrl (PXPIPE_GATEWAY_BASE_URL)",
      );
    }
    return { anthropic: `${base}/anthropic`, openai: `${base}/openai`, stripOpenAIV1: true };
  }
  return {
    anthropic: (config.upstream ?? DEFAULT_UPSTREAM).replace(/\/+$/, ''),
    openai: (config.openAIUpstream ?? DEFAULT_OPENAI_UPSTREAM).replace(/\/+$/, ''),
    stripOpenAIV1: false,
  };
}

/** Parse `PXPIPE_GATEWAY_HEADERS` — JSON object or `k=v;k2=v2`. */
export function parseGatewayHeaders(spec: string | undefined): Record<string, string> {
  if (!spec) return {};
  const trimmed = spec.trim();
  if (trimmed.startsWith('{')) {
    const obj = JSON.parse(trimmed) as Record<string, unknown>;
    const out: Record<string, string> = {};
    for (const [k, v] of Object.entries(obj)) out[k] = String(v);
    return out;
  }
  const out: Record<string, string> = {};
  for (const pair of trimmed.split(';')) {
    const i = pair.indexOf('=');
    if (i <= 0) continue;
    out[pair.slice(0, i).trim()] = pair.slice(i + 1).trim();
  }
  return out;
}

/** Build the proxy fetch handler bound to a config. */
export function createProxy(config: ProxyConfig = {}) {
  const routes = resolveUpstreams(config);
  const upstream = routes.anthropic;
  const openAIUpstream = routes.openai;
  const gatewayHeaders = config.gatewayHeaders ?? {};
  const applyGatewayHeaders = (h: Headers): Headers => {
    for (const [k, v] of Object.entries(gatewayHeaders)) h.set(k, v);
    return h;
  };

  return async function handle(req: Request): Promise<Response> {
    const t0 = Date.now();
    const url = new URL(req.url);
    const path = url.pathname + url.search;

    // Captured during the transform step. `reqBodyBytes` is the raw
    // transformed body — kept around so we can gzip it lazily on 4xx without
    // having to re-stringify. `reqBodySha8` is computed eagerly because
    // it's cheap and lands on every event (4xx and 2xx) for correlation.
    let reqBodyBytes: Uint8Array | undefined;
    let reqBodySha8: string | undefined;

    const fire = (
      status: number,
      info?: TransformInfo,
      error?: string,
      firstByteMs?: number,
      usage?: Usage,
      errorBody?: string,
      measurement?: OutputMeasurement,
    ): void => {
      const is4xx = status >= 400 && status < 500;
      // Gzip the full body only when we actually need it — i.e. status is 4xx
      // and we have bytes to capture. Awaiting inside an async IIFE keeps the
      // fire() signature unchanged; the host receives the event once the
      // gzip resolves (or immediately if not 4xx).
      const finalize = async (): Promise<void> => {
        let reqBodyGz: Uint8Array | undefined;
        if (is4xx && reqBodyBytes && reqBodyBytes.byteLength > 0) {
          try {
            reqBody
[assistant]
Reviewed src/core/proxy.ts.
[user]
final call after benchmarks: store layer goes with zustand; valtio rejected, bundle delta too big.
[assistant]
Locked in: zustand.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
s ` +
    `(${args.originalLines.toLocaleString('en-US')} lines, ~${args.originalEstImages} images).` +
    `${tailNote} ]\n\n`
  );
}

/** Truncate `text` so it renders to roughly `maxImages` images at the given
 *  `cols`. Picks head/tail split based on `classifyContent`. Budget measured
 *  in visual rows (what render.ts actually slices on). Returns the truncated
 *  text (with paging marker embedded) and the count of chars omitted. If
 *  `text` already fits, returns unchanged with `omittedChars: 0`. Exported
 *  for tests. */
export function truncateForBudget(
  text: string,
  maxImages: number,
  cols: number,
  numCols: number = 1,
  maxCharsPerImage: number = DENSE_CONTENT_CHARS_PER_IMAGE,
): { text: string; omittedChars: number; truncated: boolean } {
  const n = Math.max(1, numCols | 0);
  const estImages = estimateImageCount(text, cols, n, maxCharsPerImage);
  if (estImages <= maxImages) return { text, omittedChars: 0, truncated: false };
  const readableLinesPerCol = Math.max(1, Math.floor(READABLE_CHARS_PER_IMAGE / Math.max(1, cols)));
  const totalRowBudget = Math.max(8, maxImages * Math.min(LINES_PER_IMAGE, readableLinesPerCol) * n - 6);
  const totalCharBudget = Math.max(128, maxImages * maxCharsPerImage * n - 512);
  const shape = classifyContent(text);
  // Reflowed text uses NL_SENTINEL (↵ U+21B5) as line separator instead of \n.
  // Split on whichever delimiter the text uses so we can truncate at logical
  // line boundaries rather than treating the entire reflowed blob as one line.
  const nlChar = text.indexOf('\n') >= 0 ? '\n' : NL_SENTINEL;
  const lines = text.split(nlChar);
  const originalLines = lines.length;
  const originalChars = text.length;

  if (shape === 'structured') {
    let rows = 0;
    let chars = 0;
    let cut = 0;
    for (let i = 0; i < lines.length; i++) {
      const r = lineRows(lines[i]!, cols);
      const c = lines[i]!.length + (i > 0 ? 1 : 0);
      if (rows + r > totalRowBudget || chars + c > totalCharBudget) break;
      rows += r;
      chars += c;
      cut = i + 1;
    }
    if (cut === 0) cut = 1;
    const head = lines.slice(0, cut).join(nlChar);
    const omitted = originalChars - head.length;
    return {
      text:
        head +
        buildPagingMarker({
          originalChars,
          originalLines,
          originalEstImages: estImages,
          shownHeadLines: cut,
          shownTailLines: 0,
          omittedLines: originalLines - cut,
          omittedChars: omitted,
        }),
      omittedChars: omitted,
      truncated: true,
    };
  }

  // log / other: 60% head, 40% tail.
  const headRowBudget = Math.floor(totalRowBudget * 0.6);
  const tailRowBudget = totalRowBudget - headRowBudget;
  const headCharBudget = Math.floor(totalCharBudget * 0.6);
  const tailCharBudget = totalCharBudget - headCharBudget;
  let headRows = 0;
  let headChars = 0;
  let headCut = 0;
  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:
  
[assistant]
Reviewed src/core/proxy.ts.
[user]
ops: retry budget is exactly 9120ms, do not confuse it with the cache TTL.
[assistant]
Retry budget set: 9120ms.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
the host supplies an empirical override.
    // Same discriminator as the slab path: check the *raw* `opts` so a host
    // that genuinely wants `4` can pin to it without colliding with the merged
    // default.
    const historyCpt = opts.charsPerToken !== undefined
      ? o.charsPerToken
      : HISTORY_CHARS_PER_TOKEN;
    const horizon = Math.max(1, Math.floor(o.historyAmortizationHorizon));
    // Pass the symmetric warm-cache burn through to the history-collapse
    // gate as well. The slab gate alone got the symmetric treatment, which
    // let the history gate flip a session out of image mode even when
    // symmetric burn would have kept the slab gate in. Production data
    // 2026-05-23 showed three-turn sessions paying cache_create every
    // turn because the history gate ignored priorWarmImageTokens.
    const historyProfitable = (text: string, cols: number): boolean =>
      isCompressionProfitableAmortized(
        text, cols, undefined, 1, historyCpt, horizon,
        o.priorWarmTokens, o.priorWarmImageTokens,
      );
    const { messages: newMessages, info: histInfo } = await collapseHistory(
      req.messages,
      historyProfitable,
      { cols: o.cols },
    );
    if (histInfo.collapsedTurns > 0) {
      req.messages = newMessages;
      info.collapsedTurns = histInfo.collapsedTurns;
      info.collapsedChars = histInfo.collapsedChars;
      info.collapsedImages = histInfo.collapsedImages;
      info.imageCount += histInfo.collapsedImages;
      info.imageBytes += histInfo.collapsedImageBytes;
      info.imagePixels = (info.imagePixels ?? 0) + histInfo.collapsedImagePixels;
      info.droppedChars = (info.droppedChars ?? 0) + histInfo.droppedChars;
      for (const [cp, n] of histInfo.droppedCodepoints) {
        droppedCodepoints.set(cp, (droppedCodepoints.get(cp) ?? 0) + n);
      }
      info.historyReason = 'collapsed';
      // Phase 1 (Task #18): per-bucket char attribution. History gets its
      // own bucket because it runs on JSON-dense prose at a different cpt
      // from system slabs and tool_results. The chars that fed the history
      // renderer are exactly what `collapsedChars` already tracks.
      info.historyTextChars = histInfo.collapsedChars;
      info.historyImageSha = await historyImageSha8(newMessages);
      bumpBucket(info, 'history', histInfo.collapsedChars);
    } else if (histInfo.reason) {
      info.historyReason = histInfo.reason;
    }
  }

  info.compressed = true;
  // Serialize the top dropped codepoints (if any) as `U+HHHH` → count. Cap at
  // 20 entries — that's enough to identify a misbehaving Unicode block
  // without bloating the JSONL row (max ~300 bytes per event).
  if (droppedCodepoints.size > 0) {
    const TOP_N = 20;
    const sorted = [...droppedCodepoints.entries()]
      .sort((a, b) => b[1] - a[1])
      .slice(0, TOP_N);
    const out: Record<string, number> = {};
    for (const [cp, count] of sorted) {
      const hex = cp.toString(16).toUpperCase().padStart(4, '0');
      out[`U+${hex}`] = count;
    }
    info.droppedCodepointsTop = out;
  }
  // Empirical-cost telemetry: count every char of TEXT remaining in the
  // outgoing body (system text blocks + every TextBlock across messages).
  // Pairs with `imagePixels` and the upstream usage so a regression over
  // N cold-miss events solves `tokens ≈ α·outgoingTextChars + β·imagePixels`
  // for the empirical chars/token and pixels/token under the live model.
  info.outgoingTextChars = countOutgoingTextChars(req);
  const outBody = new TextEncoder().encode(JSON.stringify(req));
  return { body: outBody, info };
}

/** Walk the outgoing transformed request body and sum the length of every
 *  char the upstream tokenizer will see as text. Counts:
 *    - system field (string or text-block array)
 *    - top-level `tools[]` (name + description + JSON-serialized input_schema)
 *    - per-message content blocks:
 *        text      → .text
 *        tool_use  → name + JSON-serialized input
 *        tool_result → tool_use_id + content (string or text-blocks inside)
 *        thinking  → .thinking  (extended-thinking blocks, Opus/Sonnet 4.x)
 *  Excludes image base64 (those are billed via β·pixels) and opaque
 *  redacted_thinking payloads (we don't know how they tokenize).
 *
 *  This count is the denominator in `tokens ≈ α·outgoingTextChars +
 *  β·imagePixels`
[assistant]
Reviewed src/core/render.ts.
[assistant]
Root cause found: the double-flush race is in src/cursor/core.ts; src/cursor/io.ts was only the symptom site.
[user]
fix only the root cause file.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
 rather than stale
   * lifetime aggregates from a previous run.
   *
   * Returns `{ sessionId: null, message: 'no active session yet' }` when no
   * events have been received yet (or the first events were all untagged —
   * cold start, probe failures) — `update()` only sets `currentSessionId`
   * when a `firstUserSha8`-tagged event lands. The client renders a stale
   * panel rather than zeroes when a session goes idle (NO `lastSeen >
   * threshold` check here; see comment in `update()` for the rationale).
   */
  serveCurrentSessionJson(): Response {
    if (!this.currentSessionId) {
      return jsonResponse({
        sessionId: null,
        message: 'no active session yet',
      });
    }
    const s = this.sessions.get(this.currentSessionId);
    if (!s) {
      return jsonResponse({ sessionId: null, message: 'no active session yet' });
    }
    // Headline payload: the same dollar-weighted baseline/actual input
    // accumulators the global Totals block exposes, plus the honest
    // denominator (`baselineMeasuredCount` — only requests that carried a
    // baseline measurement). We ALSO ship the ALL-rows session bill
    // (`allActualInputWeighted` + `allOutputWeighted`) so the Svelte panel
    // can compute saved-% against the full session bill instead of just
    // the measured slice — matching the global `saved_pct_of_all_spend`
    // math but scoped to one session. The Svelte panel does the dollar
    // conversion itself so we don't round-trip pricing through the wire.
    return jsonResponse({
      sessionId: s.sessionId,
      baselineInputWeighted: s.baselineInputWeighted,
      actualInputWeighted: s.actualInputWeighted,
      baselineMeasuredCount: s.baselineMeasuredCount,
      allActualInputWeighted: s.allActualInputWeighted,
      allOutputWeighted: s.allOutputWeighted,
    });
  }

  serveStats(): Response {
    // Two headline numbers, derived from the same per-event accumulators:
    //
    //   saved_pct_input_only = Σ saved / Σ baseline_input_eff × 100
    //     What the proxy actually saved on the slice it can move (input).
    //     Numerator = input tokens we didn't pay for (cache-aware).
    //     Denominator = input tokens we WOULD have paid (cache-aware).
    //     Output is excluded because the proxy doesn't touch it.
    //
    //   saved_pct_of_total_bill = Σ saved / Σ (baseline_input + output × 5) × 100
    //     What share of the TOTAL bill the proxy saved. Honest counter to the
    //     input-only number: on output-heavy sessions (long thinking blocks,
    //     big edits) the percentage shrinks because output dominates.
    //
    //   token_equivalent_total = Σ (actual_input + output × 5)
    //     What Anthropic's weekly limit actually meters — input × 1.0 +
    //     output × 5.0 (the same ratio as the per-MTok price card). This is
    //     the number that moves your "%% used this week" indicator.
    const baseline = this.totals.baselineInputWeighted;
    const actual = this.totals.actualInputWeighted;
    const output = this.totals.outputWeighted; // already × OUTPUT_TOKEN_RATE
    const saved = baseline - actual;
    const pctInput = baseline > 0 ? (saved / baseline) * 100 : 0;
    const baselineTotal = baseline + output;
    const actualTotal = actual + output;
    const pctTotal = baselineTotal > 0 ? (saved / baselineTotal) * 100 : 0;

    // Share-of-all-spend: honest denominator. The numerator can only credit
    // savings against rows where we have a probe baseline (otherwise it's
    // estimation), but the denominator MUST include every request the user
    // actually paid for — including passthrough rows, probe-failed rows,
    // and untransformed turns the gate said no to. Otherwise the headline
    // answers "did pxpipe help on the rows where it ran" instead of
    // "did pxpipe move my real bill". The first is a cherry-pick.
    const allBaselineEquiv = this.totals.allBaselineEquivalentWeighted;
    const allActual = this.totals.allActualInputWeighted;
    const allOutput = this.totals.allOutputWeighted;
    // Denominator = counterfactual all-rows bill: what the user would have
    // paid with no pxpipe. Bounded ratio at 100%; a single cold-miss
    // compressed request on an otherwise empty session shows ~99% saved,
    // not 280%.
    const allCounterfactualBill = allB
[assistant]
Reviewed src/core/render.ts.
[user]
routing: the on-call REVIEWER is Soren Nakamura; Tobias Petrov stays author and cannot self-review.
[assistant]
PR review to Soren Nakamura.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
 image block carried by the synthetic
 * history message. `collapseHistory` returns `[syntheticUser, ...tail]`, so
 * the history images — if any — live on `messages[0]`.
 *
 * Logging this per request makes the cache-key drift bug (#28) observable
 * straight from `events.jsonl`: while the quantized collapse boundary holds,
 * consecutive collapsed events MUST report an identical `history_image_sha8`.
 * That byte-stability is exactly what lets Anthropic's prompt cache serve the
 * history prefix as a `cache_read` (0.1x) instead of re-billing a fresh
 * `cache_create` (1.25x) every turn. A hash that moves turn-over-turn is the
 * signature of the regression — the proxy can't *see* Anthropic's cache
 * decision, so this hash is our ground-truth proxy for it.
 *
 * Returns `undefined` when `messages[0]` carries no image blocks (i.e. no
 * collapse happened this request) — callers gate on `collapsedTurns` anyway.
 */
async function historyImageSha8(
  messages: Message[],
): Promise<string | undefined> {
  const synthetic = messages[0];
  if (!synthetic || !Array.isArray(synthetic.content)) return undefined;
  let concat = '';
  for (const blk of synthetic.content) {
    if (blk.type === 'image') concat += blk.source.data;
  }
  return concat ? sha8(concat) : undefined;
}

/**
 * Best-effort: pull out the CLAUDE.md slab from a system text. Heuristic —
 * Claude Code typically wraps it with a heading like "Claude Code Rules"
 * or includes it under a `# CLAUDE.md` / system-reminder block. Returns
 * empty string if nothing CLAUDE.md-shaped is detected; callers should
 * skip hashing in that case.
 */
export function extractClaudeMdSlab(staticText: string): string {
  if (!staticText) return '';
  // Common markers Claude Code uses around the CLAUDE.md content.
  const startPatterns = [
    /^\s*#+\s*Claude\s+Code\s+Rules\s*$/im,
    /^\s*#+\s*CLAUDE\.md\s*$/im,
    /^\s*Claude\s+Code\s+Rules:?\s*$/im,
  ];
  let startIdx = -1;
  for (const p of startPatterns) {
    const m = p.exec(staticText);
    if (m && (startIdx === -1 || m.index < startIdx)) startIdx = m.index;
  }
  if (startIdx === -1) return '';
  // Run until the next top-level heading (# foo) or end of text.
  const tail = staticText.slice(startIdx);
  const endMatch = /\n#\s+\S/.exec(tail.slice(1));
  const end = endMatch ? endMatch.index + 1 : tail.length;
  return tail.slice(0, end).trim();
}

/**
 * Hash the first user message text, capped at 4 KiB so very long initial
 * pastes don't dominate hashing time and so we still get a stable id for
 * the conversation thread (initial prompt usually fits well within 4 KiB).
 */
export function firstUserText(req: MessagesRequest): string {
  const msgs = req.messages ?? [];
  for (const m of msgs) {
    if (m.role !== 'user') continue;
    if (typeof m.content === 'string') return m.content.slice(0, 4096);
    if (Array.isArray(m.content)) {
      for (const block of m.content) {
        if (block && (block as any).type === 'text' && typeof (block as any).text === 'string') {
          return ((block as any).text as string).slice(0, 4096);
        }
      }
    }
    // First user message found but unreadable → return empty so we don't
    // accidentally hash some downstream user message.
    return '';
  }
  return '';
}

/**
 * Pull structured fields out of the dynamic slab. Only reads — does not
 * modify the text. Used purely for telemetry / improvement signals.
 */
export function extractEnvFields(dynamicText: string): EnvFields {
  const out: EnvFields = {};
  if (!dynamicText) return out;

  const envMatch = /<env>([\s\S]*?)<\/env>/i.exec(dynamicText);
  if (envMatch) {
    const body = envMatch[1]!;
    const cwd = /(?:^|\n)\s*Working directory:\s*(.+?)\s*(?:\n|$)/i.exec(body);
    if (cwd) out.cwd = cwd[1]!.trim();
    const gitRepo = /(?:^|\n)\s*Is directory a git repo:\s*(Yes|No)\b/i.exec(body);
    if (gitRepo) out.isGitRepo = gitRepo[1]!.toLowerCase() === 'yes';
    const platform = /(?:^|\n)\s*Platform:\s*(.+?)\s*(?:\n|$)/i.exec(body);
    if (platform) out.platform = platform[1]!.trim();
    const osVer = /(?:^|\n)\s*OS Version:\s*(.+?)\s*(?:\n|$)/i.exec(body);
    if (osVer) out.osVersion = osVer[1]!.trim();
    const today = /(?:^|\n)\s*Today'?s date:\s*(.+?)\s*(?:\n|$)/i.exec(body);
    if (today) out.today = today[1]!.trim();
  }

  // Git branch may
[assistant]
Reviewed src/core/transform.ts.
[user]
important: in PROD, HOT_RELOAD_V2 was NOT enabled, prod dashboard showed stale config cache.
[assistant]
Confirmed: HOT_RELOAD_V2 OFF in prod, ON only in staging.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
ssage:
 *
 *   { 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
 * unmarked; the caller in `transform.ts` decides placement.
 *
 * Spec source: `/tmp/pxpipe-history-compression.md` Variant C section
 * (round 3, lines 346-364 + check-3 cache-control discussion).
 */

import type { ContentBlock, ImageBlock, Message, TextBlock, ToolUseBlock, ToolResultBlock } from './types.js';
import { DENSE_CONTENT_CHARS_PER_IMAGE, DENSE_CONTENT_COLS, DENSE_RENDER_STYLE, renderTextToPngsWithCharLimit } from './render.js';
import { bytesToBase64 } from './png.js';

/** Function predicate signature for the break-even gate. Passed in by the
 *  caller (transform.ts) rather than imported here to keep `src/core/history.ts`
 *  free of a cycle with `src/core/transform.ts`. transform.ts already imports
 *  history.ts to invoke `collapseHistory`; importing back the other way would
 *  create an evaluation-order trap.
 *
 *  IMPORTANT — takes the full `text`, NOT `text.length`. The downstream
 *  `isCompressionProfitable` has two paths: a row-aware path for strings
 *  (matches renderTextToPngs() image budgeting exactly) and a looser
 *  chars-only fallback for numbers (assumes dense lines, no newlines).
 *  History text is *newline-heavy* — `--- role ---` headers, JSON args,
 *  `[tool_use]` / `[tool_result]` labels — so the chars-only estimate
 *  under-predicts image count by ~5-10× and used to let net-losers
 *  through. The 2026-05-19 production -250% savings measurement traces
 *  back to that asymmetry. Always pass the string. */
export type ProfitableFn = (text: string, cols: number) => boolean;

/** Configuration for history collapse. */
export interface HistoryCollapseOptions {
  /** Number of turns at the tail (most recent) to KEEP as text. Default 4. */
  keepTail: number;
  /** Minimum number of turns in the collapsable prefix before we attempt
   *  the rolling-window re-roll. Below this, leaving them as text costs
   *  almost nothing and the cache-amortization math doesn't work. Default 10. */
  minCollapsePrefix: number;
  /** Soft-wrap column count for the renderer. Should match the host's
   *  configured `cols` so the history image visually matches the system
   *  image. Default 100. */
  cols: number;
  /** Quantize the collapse boundary onto a fixed grid of this many
   *  messages. The collapsed prefix only advances in `collapseChunk`-sized
   *  steps, so the rendered history image stays byte-identical between
   *  steps and keeps hitting Anthropic's prompt cache instead of forcing a
   *  fresh `cache_create` (1.25x) of the whole prefix on every single turn.
   *  Set to 0 for the legacy per-turn moving boundary. Default 50. */
  collapseChunk: number;
}

export const HISTORY_DEFAULTS: HistoryCollapseOptions = {
  keepTail: 4,
  minCollapsePrefix: 10,
  cols: 100,
  collapseChunk: 50,
};

/** Per-request telemetry surfaced back to TransformInfo. */
export interface HistoryCollapseInfo {
  /** Number of turns collapsed into the history image. */
  collapsedTurns: number;
  /** Total chars of text that went into the history image. */
  collapsedChars: number;
  /** Number of PNG image blocks emitted for the history (≥1 if collapsed). */
  collapsedImages: number;
  /** Total PNG bytes emitted. */
  collapsedImageBytes: number;
  /** Total pixel area emitted (`Σ width × height`). Pairs with cold-miss
   *  cache_create tokens for empirical px/token derivation — same role as
   *  `info.imagePixels` in TransformInfo, accumulated here so the caller
   *  can fold history images into the same regression. */
  collapsedImagePixels: number;
  /** Why we didn't collapse — populated only when no collapse happened. */
  reason?:
    | 'no_history'
    | 'prefix_too_short'
    | 'no_closed_prefix'
    | 'not_profitable'
    | 'render_empty';
  /** Dropped codepoints from the history render, merged into the
   *  transform-wide map by the caller. */
  droppedChars: number;
  droppedCodepoints: Map<number, number>;
}


/**
 * Compute the largest index `i*` in `[0..messages.length - keepTail - 1]`
 * such that all `tool_use_id`s issued by assistant turns in `[0..i*]` are
 * matched by `tool_result`s also in `[0..i*]`. Returns `-1` if no such
 * boundary exists (i.e. every potential boundary has a tool_use straddling
 * into the live tail).
 *
 * Algorithm: walk left-to-right. Maintain an `openSet` of unmatched
 * tool_use_ids. After processing each message, record the current openSet
 * size. The closed-prefix boundary is the **last** index ≤ cutoff at which
 * openSet was empty AFTER processing.
 *
 * NOTE: this is robust to interleaved tool_use sequences (e.g. two parallel
 * tool calls in one assistant turn followed by two tool_results in the
 * next user turn). The openSet tracking handles that correctly.
 */
export function findClosedPrefixBoundary(
  messages: Message[],
  cutoffExclusive: number,
): number {
  if (cutoffExclusive <= 0) return -1;
  const openSet = new Set<string>();
  let lastClosed = -1;
  const limit = Math.min(cutoffExclusive, messages.length);
  for (let i = 0; i < limit; i++) {
    const msg = messages[i]!;
    if (!Array.isArray(msg.content)) {
      // Plain string content — no tool blocks possible. Just close-or-stay.
      if (openSet.size === 0) lastClosed = i;
      continue;
    }
    if (msg.role === 'assistant') {
      for (const blk of msg.content) {
        if (blk && (blk as ToolUseBlock).type === 'tool_use') {
          const id = (blk as ToolUseBlock).id;
          if (typeof id === 'string') openSet.add(id);
        }
      }
    } else if (msg.role === 'user') {
      for (const blk of msg.content) {
        if (blk && (blk as ToolResultBlock).type === 'tool_result') {
          const id = (blk as ToolResultBlock).tool_use_id;
          if (typeof id === 'string') openSet.delete(id);
        }
      }
    }
    if (openSet.size === 0) lastClosed = i;
  }
  return lastClosed;
}

/**
 * Linearise a content-block array to a single string for OCR. Drops
 * `thinking` blocks (Opus 4.7+ only requires bit-perfect on the most-recent
 * assistant-with-tool_use, which is in the live tail by construction).
 * Tool-use input args and tool-result content are included so the model
 * has full context. Inline images and tool_result images are reduced to a
 * `[image]` placeholder — embedding them in the history image would
 * double-encode for 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;
      
[assistant]
Reviewed src/core/proxy.ts.

=== end ===
