=== session s1 transcript ===
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
     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:
      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
[assistant]
Reviewed src/core/transform.ts.
[user]
Aiko Okafor (the patch author) thinks nanostores would be fine here, docs are nice.
[assistant]
nanostores is a reasonable candidate; let me also benchmark immer.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
       if (ib && (ib as TextBlock).type === 'text' && typeof (ib as TextBlock).text === 'string') {
              n += (ib as TextBlock).text.length;
            }
          }
        }
        continue;
      }

      // Extended-thinking blocks: { type: 'thinking', thinking: string, ... }
      // Not in our local types yet (we don't rewrite them), but they carry
      // real characters that the upstream tokenizer sees.
      if (type === 'thinking') {
        const th = b as unknown as { thinking?: unknown };
        if (typeof th.thinking === 'string') n += (th.thinking as string).length;
        continue;
      }

      // image, redacted_thinking, server_tool_use, etc. — skip. Either
      // billed via pixels (image) or opaque to us (redacted_thinking).
    }
  }

  return n;
}

/** JSON.stringify, but tolerant of cycles / non-serializable values.
 *  We only care about the LENGTH; if it blows up we just return 0 rather
 *  than crash the whole transform. */
function safeStringifyLen(v: unknown): number {
  try {
    return JSON.stringify(v)?.length ?? 0;
  } catch {
    return 0;
  }
}
/**
 * The pxpipe proxy as a single Web-standard fetch handler.
 *
 * Both `src/node.ts` and `src/worker.ts` adapt this to their respective
 * runtimes (node:http server vs CF Worker `fetch` export). The handler
 * itself only uses `Request`, `Response`, `URL`, and global `fetch` — all
 * of which exist identically in Node 18+ and Workers.
 */

import { transformRequest, type TransformOptions, type TransformInfo } from './transform.js';
import { transformOpenAIChatCompletions } from './openai.js';
import { isPxpipeSupportedGptModel, isPxpipeSupportedModel } from './applicability.js';
import {
  buildBaselineCountTokensBody,
  buildCacheablePrefixCountTokensBody,
} from './measurement.js';
import type { Usage } from './types.js';

export interface ProxyConfig {
  /** Provider mode. 'cloudflare-ai-gateway' derives both upstreams from
   *  `gatewayBaseUrl` (`{base}/anthropic` and `{base}/openai`) and rewrites
   *  OpenAI paths to the gateway's shape (`/v1/chat/completions` →
   *  `/chat/completions`). Anthropic paths keep their `/v1/...` shape.
   *  Unrecognized paths pass through to the family route untouched. */
  provider?: 'cloudflare-ai-gateway';
  /** Gateway base URL (account/gateway-scoped). Required when provider is
   *  set. Comes from env/config only — never hardcoded. Overrides
   *  `upstream`/`openAIUpstream`. */
  gatewayBaseUrl?: string;
  /** Extra headers injected on every upstream request (e.g. gateway auth
   *  headers). Values come from env/config only. */
  gatewayHeaders?: Record<string, string>;
  /** Anthropic API base, no trailing slash. Defaults to api.anthropic.com. */
  upstream?: string;
  /** Override or supply an API key. If unset, we forward whatever the client sent. */
  apiKey?: string;
  /** OpenAI API base for GPT chat completions, no trailing slash. */
  openAIUpstream?: string;
  /** Override or supply an OpenAI API key. If unset, we forward Authorization. */
  openAIApiKey?: string;
  /** Per-request transform options. Pass a function when the host wants to
   *  inject DYNAMIC values per request (e.g. live empirical `charsPerToken`
   *  from the dashboard's converging fit) — the proxy invokes it once per
   *  /v1/messages POST. Static object form is used by the Workers host and
   *  tests that don't need dynamic state. */
  transfo
[assistant]
Reviewed src/core/render.ts.
[assistant]
Note: the cache TTL is 2830ms, unrelated to the retry budget discussion.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
t srcOff = ATLAS_GRAY_OFFSETS[rank]!;
  for (let gy = 0; gy < ATLAS_GRAY_CELL_H; gy++) {
    const dstRow = (y + gy) * fbW + x;
    const srcRow = srcOff + gy * srcW;
    for (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: Rend
[assistant]
Reviewed src/core/transform.ts.
[assistant]
The symptom first appeared in src/retry/io.ts (stack trace top frame), still tracing root cause.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
*/
  dynamicBlockCount: number;
  /** Tag-shaped blocks found in the *static* slab that are NOT in
   *  DYNAMIC_BLOCK_TAGS. Early-warning canary: if Claude Code ships a new
   *  per-turn tag, it'll show up here before our cache hit rate collapses. */
  unknownStaticTags?: string[];
  /** Parsed env block, if Claude Code injected one. Useful for telemetry
   *  (per-project compression ratios, etc.). */
  env?: EnvFields;
  /** sha256[0..8] of the static slab + tool docs (what ends up in the image).
   *  Repeats across turns → cache_control SHOULD be hitting upstream. */
  systemSha8?: string;
  /** sha256[0..8] of just the CLAUDE.md section if detectable. Lets us
   *  bucket requests by project even when cwd is absent. */
  claudeMdSha8?: string;
  /** sha256[0..8] of the first user message text (first 4 KiB). Rough
   *  thread/session id since the wire protocol carries none. */
  firstUserSha8?: string;
  /** Raw bytes of the FIRST rendered image. Used by the in-process dashboard
   *  to show a preview. NOT persisted to JSONL (toTrackEvent drops it). */
  firstImagePng?: Uint8Array;
  /** Pixel dimensions of the first image. */
  firstImageWidth?: number;
  firstImageHeight?: number;
  /** Every rendered PNG for this request, in render order. images[0] === firstImagePng.
   *  Surfaced separately so the dashboard can pin any image individually. */
  imagePngs?: Uint8Array[];
  /** Matching pixel dimensions for each entry in imagePngs. */
  imageDims?: Array<{ width: number; height: number }>;
  /** The source text that was rendered into `imagePngs` (the combined
   *  slab text, header included). Lets the dashboard show the before/after
   *  pair so an operator can see exactly what JSON/tool-result text became
   *  the image. Capped at 64 KiB to bound memory; NOT persisted to JSONL
   *  (toTrackEvent drops it alongside the PNG bytes). */
  imageSourceText?: string;
  /** Number of images we added by compressing `<system-reminder>` blocks in
   *  the first user message. */
  reminderImgs?: number;
  /** Number of images we added by compressing tool_result content across
   *  user messages. */
  toolResultImgs?: number;
  /** Codepoints in the rendered text that weren't in the atlas. They
   *  rendered as blank cells. A non-zero count means the user is producing
   *  glyphs we don't ship — useful telemetry for tuning the atlas profile
   *  (e.g. switch from `practical` → `full-bmp` if Hangul shows up). */
  droppedChars?: number;
  /** Top dropped codepoints by frequency for this request, keyed `U+HHHH`
   *  (uppercase hex, at least 4 digits). At most 20 entries, sorted by count
   *  descending. Only set when `droppedChars > 0`. Lets the operator
   *  identify which Unicode blocks to add to the atlas profile without
   *  having to capture & inspect the request body. */
  droppedCodepointsTop?: Record<string, number>;
  /** Counters for why blocks didn't get image-compressed this request.
   *  Helps tune the break-even check vs the flat threshold:
   *    - `below_threshold`: block below `minReminderChars` / `minToolResultChars`
   *      (the fast-path skip; saves CPU on obvious-no cases)
   *    - `not_profitable`: block above the threshold but `isCompressionProfitable`
   *      returned false (image cost ≥ text cost at current cell config)
   *  Only emitted when at least one counter is > 0. */
  passthroughReasons?: { below_threshold?: number; not_profitable?: number };
  /** Per-gate-call diagnostics — ex
[assistant]
Reviewed src/core/proxy.ts.
[user]
staging note: USE_BROTLI IS enabled in staging since Tuesday.
[assistant]
Ack, USE_BROTLI on in staging.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
 landed at 7×10 (96 % char accuracy vs ~82 % at naïve 5×8
 *  on dense text), but the later combination of packed reflow + grayscale
 *  atlas + the in-image instruction band (`reflow-inimage`) brought 5×8 back
 *  to 98.95 % on Opus 4.7 — slightly above the text-only baseline — so the
 *  production default reverted to the dense cell. RenderStyle.cellWBonus /
 *  cellHBonus override these (eval use only); with no style the renderer
 *  produces 5×8 cells. */
export const DEFAULT_CELL_W_BONUS = 0;
export const DEFAULT_CELL_H_BONUS = 0;
/** Effective production render-cell pixel dimensions (atlas glyph + default
 *  padding). transform.ts derives its image-budget and break-even math from
 *  these so the gate always tracks the renderer's real geometry. */
export const CELL_W = ATLAS_CELL_W + DEFAULT_CELL_W_BONUS;
export const CELL_H = ATLAS_CELL_H + DEFAULT_CELL_H_BONUS;

export interface RenderedImage {
  /** Raw PNG bytes. */
  png: Uint8Array;
  /** Pixel width. */
  width: number;
  /** Pixel height. */
  height: number;
  /** How many input *codepoints* were rendered into this image (covers wide
   *  chars correctly: 中 counts as 1, not 2). */
  charsRendered: number;
  /** Codepoints encountered that aren't in the atlas. They were rendered as
   *  blank cells; the caller may want to surface this as telemetry so a
   *  spike of drops triggers a profile review. */
  droppedChars: number;
  /** Histogram of dropped codepoints: codepoint → count for this render. The
   *  caller can merge across multiple renders to find the top offenders.
   *  Empty when droppedChars === 0; never undefined so callers don't need to
   *  null-check before iterating. */
  droppedCodepoints: Map<number, number>;
}

/** Optional render-time styling. With every field unset the renderer renders
 *  at the production default 5×8 cell (see DEFAULT_CELL_W_BONUS /
 *  DEFAULT_CELL_H_BONUS). The eval harness overrides these per variant to
 *  A/B structure aids and cell sizes against OCR fidelity on densely-packed
 *  (reflowed) text. */
export interface RenderStyle {
  /** Draw faint grey grid rules. Zero added pixels — see `drawGrid`. */
  grid?: boolean;
  /** Draw a vertical grid rule every N columns. 0/unset = row rules only. */
  gridCols?: number;
  /** Horizontal size multiplier for the ↵ newline marker. 1 = off. */
  markerScale?: number;
  /** Render the ↵ marker in red (switches the PNG to RGB truecolor). */
  markerRed?: boolean;
  /** Blank pixel rows over the 8px atlas glyph (cell height = 8 + this). The
   *  glyph bitmap stays 8px tall; this widens the vertical pitch. Unset =
   *  DEFAULT_CELL_H_BONUS (production 5×8 cell). */
  cellHBonus?: number;
  /** Blank pixel columns over the 5px atlas glyph (cell width = 5 + this).
   *  The glyph bitmap stays 5px wide; a negative value makes adjacent glyphs
   *  overlap. Unset = DEFAULT_CELL_W_BONUS (production 5×8 cell). */
  cellWBonus?: number;
  /** Use the anti-aliased grayscale atlas (atlas-gray.ts) instead of the
   *  default 1-bit atlas. EVAL-ONLY — gated on this flag; the default path
   *  (aa unset/false) is byte-identical to the pre-AA renderer. */
  aa?: boolean;
  /** Draw each successive glyph in a cycling palette color so the vision
   *  encoder gets a per-character boundary cue. Forces RGB output. Glyph
   *  shape/size unchanged. Composes with `aa: true` (AA coverage is blended
   *  onto a white background in the palette color). */
  colorCycle?: boolean;
}

// --- column-aware wrapping -------------------------------------------------

/** Visual width of a codepoint in cells (1 = Latin, 2 = East Asian Wide).
 *  Codepoints not in the atlas advance by 1 cell — they render as blank but
 *  occupy space so wrap math is stable. */
function cellsFor(codepoint: number, markerScale: number = 1): number {
  // The enlarged ↵ marker is scaled horizontally, so it occupies `markerScale`
  // cells of wrap budget instead of one.
  if (codepoint === NL_SENTINEL_CP && markerScale > 1) return markerScale;
  const rank = atlasRank(codepoint);
  if (rank < 0) return 1;
  return ATLAS_WIDE_FLAGS[rank] === 1 ? 2 : 1;
}

/** Default tab width when expanding `\t` to spaces. 4 is what GitHub, GNU
 *  cat -t, and most editors render by default. Anything else would surprise
 *  the reader, and our content (logs, code, tool output) is ~always
 *  4-space-tab-stop oriented
[assistant]
Reviewed src/core/transform.ts.
[user]
final call after benchmarks: store layer goes with immer; nanostores rejected, bundle delta too big.
[assistant]
Locked in: immer.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
ction ships the BARE cell — both bonuses are 0. The L1 OCR
 *  sweep originally landed at 7×10 (96 % char accuracy vs ~82 % at naïve 5×8
 *  on dense text), but the later combination of packed reflow + grayscale
 *  atlas + the in-image instruction band (`reflow-inimage`) brought 5×8 back
 *  to 98.95 % on Opus 4.7 — slightly above the text-only baseline — so the
 *  production default reverted to the dense cell. RenderStyle.cellWBonus /
 *  cellHBonus override these (eval use only); with no style the renderer
 *  produces 5×8 cells. */
export const DEFAULT_CELL_W_BONUS = 0;
export const DEFAULT_CELL_H_BONUS = 0;
/** Effective production render-cell pixel dimensions (atlas glyph + default
 *  padding). transform.ts derives its image-budget and break-even math from
 *  these so the gate always tracks the renderer's real geometry. */
export const CELL_W = ATLAS_CELL_W + DEFAULT_CELL_W_BONUS;
export const CELL_H = ATLAS_CELL_H + DEFAULT_CELL_H_BONUS;

export interface RenderedImage {
  /** Raw PNG bytes. */
  png: Uint8Array;
  /** Pixel width. */
  width: number;
  /** Pixel height. */
  height: number;
  /** How many input *codepoints* were rendered into this image (covers wide
   *  chars correctly: 中 counts as 1, not 2). */
  charsRendered: number;
  /** Codepoints encountered that aren't in the atlas. They were rendered as
   *  blank cells; the caller may want to surface this as telemetry so a
   *  spike of drops triggers a profile review. */
  droppedChars: number;
  /** Histogram of dropped codepoints: codepoint → count for this render. The
   *  caller can merge across multiple renders to find the top offenders.
   *  Empty when droppedChars === 0; never undefined so callers don't need to
   *  null-check before iterating. */
  droppedCodepoints: Map<number, number>;
}

/** Optional render-time styling. With every field unset the renderer renders
 *  at the production default 5×8 cell (see DEFAULT_CELL_W_BONUS /
 *  DEFAULT_CELL_H_BONUS). The eval harness overrides these per variant to
 *  A/B structure aids and cell sizes against OCR fidelity on densely-packed
 *  (reflowed) text. */
export interface RenderStyle {
  /** Draw faint grey grid rules. Zero added pixels — see `drawGrid`. */
  grid?: boolean;
  /** Draw a vertical grid rule every N columns. 0/unset = row rules only. */
  gridCols?: number;
  /** Horizontal size multiplier for the ↵ newline marker. 1 = off. */
  markerScale?: number;
  /** Render the ↵ marker in red (switches the PNG to RGB truecolor). */
  markerRed?: boolean;
  /** Blank pixel rows over the 8px atlas glyph (cell height = 8 + this). The
   *  glyph bitmap stays 8px tall; this widens the vertical pitch. Unset =
   *  DEFAULT_CELL_H_BONUS (production 5×8 cell). */
  cellHBonus?: number;
  /** Blank pixel columns over the 5px atlas glyph (cell width = 5 + this).
   *  The glyph bitmap stays 5px wide; a negative value makes adjacent glyphs
   *  overlap. Unset = DEFAULT_CELL_W_BONUS (production 5×8 cell). */
  cellWBonus?: number;
  /** Use the anti-aliased grayscale atlas (atlas-gray.ts) instead of the
   *  default 1-bit atlas. EVAL-ONLY — gated on this flag; the default path
   *  (aa unset/false) is byte-identical to the pre-AA renderer. */
  aa?: boolean;
  /** Draw each successive glyph in a cycling palette color so the vision
   *  encoder gets a per-character boundary cue. Forces RGB output. Glyph
   *  shape/size unchanged. Composes with `aa: true` (AA coverage is blended
   *  onto a white background in the palette color). */
  colorCycle?: boolean;
}

// --- column-aware wrapping -------------------------------------------------

/** Visual width of a codepoint in cells (1 = Latin, 2 = East Asian Wide).
 *  Codepoints not in the atlas advance by 1 cell — they render as blank but
 *  occupy space so wrap math is stable. */
function cellsFor(codepoint: number, markerScale: number = 1): number {
  // The enlarged ↵ marker is scaled horizontally, so it occupies `markerScale`
  // cells of wrap budget instead of one.
  if (codepoint === NL_SENTINEL_CP && markerScale > 1) return markerScale;
  const rank = atlasRank(codepoint);
  if (rank < 0) return 1;
  return ATLAS_WIDE_FLAGS[rank] === 1 ? 2 : 1;
}

/** Default tab width when expanding `\t` to spaces. 4 is what GitHub, GNU
 *  cat -t, and most editors render by default. Anything else would su
[assistant]
Reviewed src/core/render.ts.
[user]
ops: retry budget is exactly 1330ms, do not confuse it with the cache TTL.
[assistant]
Retry budget set: 1330ms.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
hether the gate accepted or rejected — we want
 *  the denominator to reflect everything the gate saw, not just the wins. */
function bumpBucket(info: TransformInfo, bucket: BucketName, chars: number): void {
  if (chars <= 0) return;
  if (!info.bucketChars) info.bucketChars = {};
  info.bucketChars[bucket] = (info.bucketChars[bucket] ?? 0) + chars;
}

/** Map a `classifyContent` shape to a tool_result bucket name. Keeps the
 *  per-call-site code free of repeated string checks. */
function toolResultBucket(shape: 'structured' | 'log' | 'other'): BucketName {
  if (shape === 'structured') return 'tool_result_json';
  if (shape === 'log') return 'tool_result_log';
  return 'tool_result_prose';
}

/** Parsed contents of Claude Code's <env> + git status blocks. All optional —
 *  fields are only populated if the corresponding line is present. */
export interface EnvFields {
  /** Working directory at the time `claude` was launched. */
  cwd?: string;
  isGitRepo?: boolean;
  /** Current git branch, parsed from <git_status> or a "Branch:" line. */
  gitBranch?: string;
  platform?: string;
  osVersion?: string;
  /** "Today's date" as Claude Code reported it (YYYY-MM-DD). */
  today?: string;
}

export interface TransformInfo {
  compressed: boolean;
  reason?: string;
  origChars: number;
  /** Total chars of source text that were image-encoded across ALL blocks
   *  this request (static slab + reminders + tool_results). Pairs with
   *  `imageCount` for honest savings math:
   *     textTokens  = compressedChars / 4
   *     imageTokens = imageCount × 2500
   *     savings     = textTokens − imageTokens
   *  Unlike `origChars` (which is just static slab + tool docs),
   *  `compressedChars` reflects what `imageCount` actually replaced. */
  compressedChars: number;
  imageCount: number;
  imageBytes: number;
  /** Total pixel area summed across all rendered images this request
   *  (`Σ width × height`). Pairs with `cache_create_tokens` on cold-miss
   *  events to derive empirical pixels-per-token under the current model —
   *  the dashboard's `OPUS_IMAGE_TOKEN_COST` and the gate's `TOKENS_PER_IMAGE`
   *  are both stale empirical constants from a different model; this gives
   *  us the raw data to re-ground them via regression instead of guessing. */
  imagePixels?: number;
  /** Total chars of TEXT remaining in the outgoing transformed body — every
   *  TextBlock across `system`, `messages[].content`, and any tool_result
   *  text that didn't get image-compressed. Pairs with `imagePixels` and
   *  the upstream token count so we can solve for chars-per-token (α) and
   *  pixels-per-token (β) empirically: `total_tokens ≈ α·outgoingTextChars +
   *  β·imagePixels`. On a cold-miss event the upstream `cache_create_tokens`
   *  is the full LHS, so a regression over N cold-misses pins both. */
  outgoingTextChars?: number;
  /** Length of the static (cacheable) slab rendered into the image. */
  staticChars: number;
  /** Length of the dynamic (per-turn) slab kept as plain text. */
  dynamicChars: number;
  /** Number of dynamic blocks detected (<env>, <context>, etc.). */
  dynamicBlockCount: number;
  /** Tag-shaped blocks found in the *static* slab that are NOT in
   *  DYNAMIC_BLOCK_TAGS. Early-warning canary: if Claude Code ships a new
   *  per-turn tag, it'll show up here before our cache hit rate collapses. */
  unknownStaticTags?: string[];
  /** Parsed env block, if Claude Code injected one. Useful for telemetry
   *  (per-project compression ratios, etc.). */
  env?: EnvFields;
  /** sha256[0..8] of the static slab + tool docs (what ends up in the image).
   *  Repeats across turns → cache_control SHOULD be hitting upstream. */
  systemSha8?: string;
  /** sha256[0..8] of just the CLAUDE.md section if detectable. Lets us
   *  bucket requests by project even when cwd is absent. */
  claudeMdSha8?: string;
  /** sha256[0..8] of the first user message text (first 4 KiB). Rough
   *  thread/session id since the wire protocol carries none. */
  firstUserSha8?: string;
  /** Raw bytes of the FIRST rendered image. Used by the in-process dashboard
   *  to show a preview. NOT persisted to JSONL (toTrackEvent drops it). */
  firstImagePng?: Uint8Array;
  /** Pixel dimensions of the first image. */
  firstImageWidth?: number;
  firstImageHeight?: number;
  /** Every rendered PNG for this reque
[assistant]
Reviewed src/core/proxy.ts.
[assistant]
Root cause found: the double-flush race is in src/retry/core.ts; src/retry/io.ts was only the symptom site.
[user]
fix only the root cause file.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
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) {
      // ↵ renders as a glyph on the line it ends — count it in the length.
      const lineLen = (isSentinel ? i + 1 : i) - lineStart;
      rows += Math.max(1, Math.ceil(lineLen / cols));
      lineStart = i + 1;
    }
  }
  return rows;
}

/** Estimate how many images `text` will render to at the given column width.
 *  Counts soft-wrapped visual rows, which is what render.ts actually budgets
 *  against. Exported for tests + the paging gate.
 *
 *  `numCols` (default 1) packs that many text columns side-by-side per
 *  image — must match the `multiCol` setting wired through to the renderer
 *  for the math to predict the actual image count. */
export function estimateImageCount(
  textOrLen: string | number,
  cols: number,
  numCols: number = 1,
  maxCharsPerImage: number = READABLE_CHARS_PER_IMAGE,
): number {
  const n = Math.max(1, numCols | 0);
  const readableLinesPerCol = Math.max(1, Math.floor(READABLE_CHARS_PER_IMAGE / Math.max(1, cols)));
  const linesPerImage = Math.min(LINES_PER_IMAGE, readableLinesPerCol) * n;
  const charBudget = Math.max(1, maxCharsPerImage * n);
  if (typeof textOrLen === 'number') {
    // Back-compat shim — numeric arg gets the looser chars-based estimate.
    return Math.max(1, Math.ceil(textOrLen / charBudget));
  }
  const rows = countVisualRows(textOrLen, cols);
  return Math.max(
    1,
    Math.ceil(rows / linesPerImage),
    Math.ceil(textOrLen.length / charBudget),
  );
}

/** Classify content so we can pick a truncation strategy. Cheap heuristics on
 *  the first ~4 KiB. Returns:
 *    - `'structured'`: JSON/YAML/diff markers at the top. Truncate tail.
 *    - `'log'`: ≥30% of lines start with a log level or timestamp. Truncate middle.
 *    - `'other'`: prose, file dumps, etc. Truncate middle.
 *  Exported for tests. */
ex
[assistant]
Reviewed src/core/transform.ts.
[user]
routing: the on-call REVIEWER is Mara Khoury; Aiko Okafor stays author and cannot self-review.
[assistant]
PR review to Mara Khoury.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
e dynamic (per-turn) slab kept as plain text. */
  dynamicChars: number;
  /** Number of dynamic blocks detected (<env>, <context>, etc.). */
  dynamicBlockCount: number;
  /** Tag-shaped blocks found in the *static* slab that are NOT in
   *  DYNAMIC_BLOCK_TAGS. Early-warning canary: if Claude Code ships a new
   *  per-turn tag, it'll show up here before our cache hit rate collapses. */
  unknownStaticTags?: string[];
  /** Parsed env block, if Claude Code injected one. Useful for telemetry
   *  (per-project compression ratios, etc.). */
  env?: EnvFields;
  /** sha256[0..8] of the static slab + tool docs (what ends up in the image).
   *  Repeats across turns → cache_control SHOULD be hitting upstream. */
  systemSha8?: string;
  /** sha256[0..8] of just the CLAUDE.md section if detectable. Lets us
   *  bucket requests by project even when cwd is absent. */
  claudeMdSha8?: string;
  /** sha256[0..8] of the first user message text (first 4 KiB). Rough
   *  thread/session id since the wire protocol carries none. */
  firstUserSha8?: string;
  /** Raw bytes of the FIRST rendered image. Used by the in-process dashboard
   *  to show a preview. NOT persisted to JSONL (toTrackEvent drops it). */
  firstImagePng?: Uint8Array;
  /** Pixel dimensions of the first image. */
  firstImageWidth?: number;
  firstImageHeight?: number;
  /** Every rendered PNG for this request, in render order. images[0] === firstImagePng.
   *  Surfaced separately so the dashboard can pin any image individually. */
  imagePngs?: Uint8Array[];
  /** Matching pixel dimensions for each entry in imagePngs. */
  imageDims?: Array<{ width: number; height: number }>;
  /** The source text that was rendered into `imagePngs` (the combined
   *  slab text, header included). Lets the dashboard show the before/after
   *  pair so an operator can see exactly what JSON/tool-result text became
   *  the image. Capped at 64 KiB to bound memory; NOT persisted to JSONL
   *  (toTrackEvent drops it alongside the PNG bytes). */
  imageSourceText?: string;
  /** Number of images we added by compressing `<system-reminder>` blocks in
   *  the first user message. */
  reminderImgs?: number;
  /** Number of images we added by compressing tool_result content across
   *  user messages. */
  toolResultImgs?: number;
  /** Codepoints in the rendered text that weren't in the atlas. They
   *  rendered as blank cells. A non-zero count means the user is producing
   *  glyphs we don't ship — useful telemetry for tuning the atlas profile
   *  (e.g. switch from `practical` → `full-bmp` if Hangul shows up). */
  droppedChars?: number;
  /** Top dropped codepoints by frequency for this request, keyed `U+HHHH`
   *  (uppercase hex, at least 4 digits). At most 20 entries, sorted by count
   *  descending. Only set when `droppedChars > 0`. Lets the operator
   *  identify which Unicode blocks to add to the atlas profile without
   *  having to capture & inspect the request body. */
  droppedCodepointsTop?: Record<string, number>;
  /** Counters for why blocks didn't get image-compressed this request.
   *  Helps tune the break-even check vs the flat threshold:
   *    - `below_threshold`: block below `minReminderChars` / `minToolResultChars`
   *      (the fast-path skip; saves CPU on obvious-no cases)
   *    - `not_profitable`: block above the threshold but `isCompressionProfitable`
   *      returned false (image cost ≥ text cost at current cell config)
   *  Only emitted when at least one counter is > 0. */
  passthroughReasons?: { below_threshold?: number; not_profitable?: number };
  /** Per-gate-call diagnostics — exactly what the slab break-even gate
   *  saw and compared. Foundational observability for why a turn flipped
   *  or stayed: hosts that persist this can compute the verdict margin
   *  (`textTokens + burnTextSide − imageTokens − burnImageSide`),
   *  measure flap-prevention efficacy (`burnTextSide` > 0 rows that
   *  declined despite `imageTokens < textTokens`), and tune
   *  `historyAmortizationHorizon` against observed cache lifetimes.
   *
   *  Currently emitted for the session-anchor slab gate only. Per-block
   *  reminder / tool_result gates remain summarised in `passthroughReasons`
   *  + `bucketChars` — adding per-call diagnostics there would multiply
   *  event size without commensurate signal (those gat
[assistant]
Reviewed src/core/transform.ts.
[user]
important: in PROD, USE_BROTLI was NOT enabled, prod dashboard showed stale config cache.
[assistant]
Confirmed: USE_BROTLI OFF in prod, ON only in staging.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
rement: OutputMeasurement | undefined;
  }> => {
    const reader = forUs.getReader();
    const decoder = new TextDecoder();
    let buf = '';

    try {
      if (ct.includes('text/event-stream')) {
        // SSE: walk every event to EOF. Final output_tokens is in message_delta
        // (last event before message_stop); redacted_thinking blocks can appear
        // anywhere. Tee back-pressure is bounded by the slower-reader's buffer,
        // which here is whichever of the proxy/scanner falls behind — both run
        // at network speed in practice.
        const m: OutputMeasurement = {
          textChars: 0,
          thinkingChars: 0,
          toolUseChars: 0,
          redactedBlockCount: 0,
        };
        const state: { usage: Usage | undefined } = { usage: undefined };
        while (true) {
          const { done, value } = await reader.read();
          if (done) break;
          buf += decoder.decode(value, { stream: true });
          // Drain every complete event (terminated by a blank line per SSE spec).
          let evEnd: number;
          while ((evEnd = buf.indexOf('\n\n')) >= 0) {
            const block = buf.slice(0, evEnd);
            buf = buf.slice(evEnd + 2);
            processSseEvent(block, m, state);
          }
        }
        buf += decoder.decode();
        // Trailing partial event (no blank line) — try once for robustness.
        if (buf.trim().length > 0) processSseEvent(buf, m, state);
        return { usage: state.usage, measurement: m };
      }

      if (ct.includes('application/json')) {
        // Non-stream: buffer fully (capped at 4 MiB).
        const MAX = 4 * 1024 * 1024;
        while (buf.length < MAX) {
          const { done, value } = await reader.read();
          if (done) break;
          buf += decoder.decode(value, { stream: true });
        }
        try {
          const j = JSON.parse(buf);
          return {
            usage: normalizeUsage(j?.usage),
            measurement: measureFromMessageJson(j),
          };
        } catch {
          return { usage: undefined, measurement: undefined };
        }
      }
    } catch {
      /* tee may be released early if the client aborts — ignore */
    }
    // Unknown content-type: drain so the tee buffer doesn't hold the stream open.
    try {
      while (true) {
        const { done } = await reader.read();
        if (done) break;
      }
    } catch {
      /* ignore */
    }
    return { usage: undefined, measurement: undefined };
  })();

  return {
    response: new Response(forClient, {
      status: res.status,
      statusText: res.statusText,
      headers: res.headers,
    }),
    usagePromise: scanResult.then((s) => s.usage),
    errorBodyPromise: Promise.resolve(undefined),
    measurementPromise: scanResult.then((s) => s.measurement),
  };
}

const DEFAULT_UPSTREAM = 'https://api.anthropic.com';
const DEFAULT_OPENAI_UPSTREAM = 'https://api.openai.com';

/** Headers we strip on the way out — they're hop-by-hop or proxy-injected. */
const STRIP_REQ_HEADERS = new Set([
  'host',
  'connection',
  'keep-alive',
  'proxy-connection',
  'transfer-encoding',
  'upgrade',
  'content-length', // we recompute
  'expect',
  'accept-encoding', // let upstream choose
]);

const STRIP_RES_HEADERS = new Set([
  'connection',
  'keep-alive',
  'transfer-encoding',
  'content-encoding', // we don't re-encode
  'content-length',   // body may differ after streaming
]);

function filterHeaders(src: Headers, strip: Set<string>): Headers {
  const out = new Headers();
  src.forEach((v, k) => {
    if (!strip.has(k.toLowerCase())) 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 {
            reqBodyGz = await gzipBytes(reqBodyBytes);
          } catch {
            // gzip failure is non-fatal — drop the body sample, keep the rest.
          }
        }
        // Wait for the baseline count_tokens probes before persisting the
        // event so both numbers land on the same row as the usage block.
        // Each probe is independent: full-body baseline can land even if the
        // cacheable-prefix probe fails (and vice versa). null/missing leaves
        // the field absent; the dashboard's per-event math degrades cleanly.
        if (info && baselineStatusApplies) {
          // Track both halves of the cache-aware baseline so we can honestly
          // report whether a row is fully measured, partially measured, or
          // un-measured. Without this, a missing cacheable-prefix probe was
          // silently bucketed 
[assistant]
Reviewed src/core/proxy.ts.

=== end ===
