=== session s5: earlier coding session transcript ===
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
 for the gating.
          let baselineResolved: number | null = null;
          let cacheableExpected = false;
          let cacheableResolved: number | null = null;
          if (baselinePromise) {
            try {
              baselineResolved = await baselinePromise;
              if (baselineResolved !== null) info.baselineTokens = baselineResolved;
            } catch {
              /* probe threw — drop, keep the rest of the event intact */
            }
          }
          if (baselineCacheablePromise) {
            cacheableExpected = true;
            try {
              cacheableResolved = await baselineCacheablePromise;
              if (cacheableResolved !== null) info.baselineCacheableTokens = cacheableResolved;
            } catch {
              /* probe threw — leave field absent */
            }
          }
          if (baselineResolved === null) {
            info.baselineProbeStatus = 'failed';
          } else if (cacheableExpected && cacheableResolved === null) {
            // Body had cache_control markers but the prefix probe didn't
            // come back. The dashboard MUST NOT treat this as cacheable=0
            // (that would charge the unproxied counterfactual as if it had
            // no cache reuse, fabricating savings). It excludes the row.
            info.baselineProbeStatus = 'partial';
          } else {
            // Either both probes resolved, or the body had no markers and
            // cacheable=0 is exact by construction
[assistant]
Looked at src/core/proxy.ts; continuing with the change.
[user]
team sync outcome: we are going with redux-toolkit for the store layer, xstate was rejected because the bundle delta was too big.
[assistant]
Noted, redux-toolkit it is for the store layer; I will not add xstate.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
es + dimensions for the dashboard preview.
  // Stripped before persisting to JSONL by toTrackEvent. Memory cost is bounded
  // (we only ever keep ONE — the latest — via the dashboard's replace-on-update).
  if (images.length > 0) {
    info.firstImagePng = images[0]!.png;
    info.firstImageWidth = images[0]!.width;
    info.firstImageHeight = images[0]!.height;
    info.imagePngs = images.map((i) => i.png);
    info.imageDims = images.map((i) => ({ width: i.width, height: i.height }));
    info.imageSourceText = combinedWithHeader.slice(0, 65_536);
  }

  // 4. Splice images back into the request.
  // Cache-friendly layout:
  //   [intro text]                 ← static (helps OCR framing)
  //   [image block(s)]             ← static; LAST one carries cache_control
  //   ─── cache breakpoint ───
  //   [end-marker + dynamic + billing]  ← per-turn, NO cache_control
  //   [sysRemainder]               ← any non-text blocks the caller had
  // OCR framing (instruction header + column/reflow notes) is now baked into
  // the image itself — see `imageInstructionHeader` above. No standalone
  // TextBlock is emitted before the image. The tail closer below still sits
  // as plain text after the image so the model knows where rendered context
  // ends and per-turn dynamic content begins.
  const tailParts: string[] = ['[End of rendered context.]'];
  if (dynamicText) tailParts.push(dynamicText);
  if (billingLine) tailParts.push(billingLine);
  const tailText = tailParts.join('\n\n');

  // Image blocks ALWAYS go into the first user message — Anthropic's `s
[assistant]
Looked at src/core/proxy.ts; continuing with the change.
[user]
fyi the on-call reviewer for this change is Lucia Costa, route the PR to them.
[assistant]
Will request review from Lucia Costa.
[tool_use Read]
{"file_path":"src/core/proxy.ts"}
[tool_result]
.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
 * 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 start
[assistant]
Looked at src/core/proxy.ts; continuing with the change.
[assistant]
Found it: the double-flush race lives in src/cursor/io.ts, the lock is released before the journal write lands.
[user]
ok fix it there, nowhere else.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
E)` to the
   *  TEXT side — the cost of forcing a fresh cache_create on the
   *  un-rewritten text prefix when the rewritten image prefix was warm.
   *  Default 0 (back-compat; existing single-arg callers behave unchanged).
   *  See PxpipeOptions.priorWarmImageTokens for the foundational rationale. */
  priorWarmImageTokens: number = 0,
  /** Shrink the rendered canvas width to the longest actual wrapped line.
   *  Default `true` (per-block content: tool_result, reminder, history).
   *  Set `false` for the system slab, which deliberately fills the full
   *  configured `cols` (multi-col packing). */
  shrinkWidth: boolean = true,
): boolean {
  const n = Math.max(1, numCols | 0);
  if (typeof text !== 'string' || text.length === 0) return false;
  const cpt = Number.isFinite(charsPerToken) && charsPerToken > 0
    ? charsPerToken
    : CHARS_PER_TOKEN;
  const imageTokensCost_ = imageTokensCost(text, cols, n, imageCountCap, shrinkWidth);
  const textTokensEquivalent = text.length / cpt;
  // Cache-burn penalty (symmetric form, ANTI-FLAPPING):
  //
  //   text→image flip: invalidate the warm text cache. Burn applied to
  //                    the IMAGE side — discourages compressing when
  //                    the text prefix is already warm.
  //   image→text flip: invalidate the warm image cache. Burn applied to
  //                    the TEXT side — discourages decompressing when
  //                    the image prefix is already warm.
  //
  // Without the symmetric term the gate ping-pongs: once a session
  // commits to a mode, single-turn cost can favor flipping, but the
  // flip forces cache_create on the new side, then the next turn flips
  // back. We pay cache_create twice. The symmetric burn pins the
  // session in its current mode unle
[assistant]
Looked at src/core/render.ts; continuing with the change.
[user]
ops note: the upstream gateway hard-times-out at 10s, so set our retry budget to exactly 1250ms and do not change it without a ticket.
[assistant]
Set the retry budget constant to 1250ms.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
apped 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. */
export function classifyContent(text: string): 'structured' | 'log' | 'other' {
  const head = text.slice(0, 4096);
  const trimmed = head.trimStart();
  if (trimmed.startsWith('{') && /^\{\s*("|\})/.test(trimmed)) return 'structured';
  if (trimmed.startsWith('[') && /^\[\s*("|\{|\[|-?\d|true\b|false\b|null\b|\])/.test(trimmed))
    return 'structured';
  if (trimmed.startsWith('---\n') || trimmed.startsWith('---\r\n')) return 'structured';
  if (trimmed.startsWith('diff --git ') || /^---\s+\S/.test(trimmed)) return 'structured';
  const lines = head.split('\n').slice(0, 40).filter((l) => l.length > 0);
  if (lines.length < 4) return 'other';
  const LOG_LINE =
    /^(\[?(DEBUG|INFO|WARN|WARNING|ERROR|TRACE|FATAL)\]?\b|\d{4}-\d{2}-\d{2}[T ]?|\d{2}:\d{2}:\d{2}\b)/;
  let logHits = 0;
  for (const line of lines) if (LOG_LINE.test(line)) logHits++;
  if (logHits / lines.length >= 0.3) return 'log';
  return 'other';
}

/** Build the paging marker text. The model sees this verbatim INSIDE the
 *  rendered image so it can reason about what was elided. */
function buildPagingMarker(args: {
  originalChars: number;
  originalLines: number;
  originalEstImages: number;
  shownHeadLin
[assistant]
Looked at src/core/render.ts; continuing with the change.
[user]
important: we did NOT enable HOT_RELOAD_V2 in prod, it only looked enabled because of the stale config cache. coverage stayed at 78%.
[assistant]
Understood: HOT_RELOAD_V2 is OFF in prod, the dashboard was lying; coverage 78%.
[tool_use Read]
{"file_path":"src/core/history.ts"}
[tool_result]
s prior cache key. Default 0
   *  (cold-start behavior; matches pre-burn-aware callers byte-for-byte). */
  priorWarmTokens: number = 0,
  /** Symmetric image-side burn: tokens the rewritten (IMAGE) path would
   *  have hit cache on. Adds a one-time burn penalty of
   *  `priorWarmImageTokens × (CACHE_CREATE_RATE − CACHE_READ_RATE)` to the
   *  TEXT side — the cost of forcing a fresh cache_create on the
   *  un-rewritten text prefix when the rewritten image prefix was warm.
   *  Default 0 (back-compat; existing single-arg callers behave unchanged).
   *  See PxpipeOptions.priorWarmImageTokens for the foundational rationale. */
  priorWarmImageTokens: number = 0,
  /** Shrink the rendered canvas width to the longest actual wrapped line.
   *  Default `true` (per-block content: tool_result, reminder, history).
   *  Set `false` for the system slab, which deliberately fills the full
   *  configured `cols` (multi-col packing). */
  shrinkWidth: boolean = true,
): boolean {
  const n = Math.max(1, numCols | 0);
  if (typeof text !== 'string' || text.length === 0) return false;
  const cpt = Number.isFinite(charsPerToken) && charsPerToken > 0
    ? charsPerToken
    : CHARS_PER_TOKEN;
  const imageTokensCost_ = imageTokensCost(text, cols, n, imageCountCap, shrinkWidth);
  const textTokensEquivalent = text.length / cpt;
  // Cache-burn penalty (symmetric form, ANTI-FLAPPING):
  //
  //   text→image flip: invalidate the warm text cache. Burn applied to
  //                    the IMAGE side — discourages compressing when
  //                    the text prefix is already warm.
  //   image→text flip: invalidate the warm image cache. Burn applied to
  //                    the TEXT side — discourages decompressing when
  //                    the image prefix is already warm.
  //
  // Without the symmetric term the gate ping-pongs: once a session
  // commits to a mode, single-turn cost can favor flipping, but the
  // flip forces cache_create on the new side, then the next turn flips
  // back. We pay cache_create twice. The symmetric burn pins the
  // session in its current mode unless the per-turn delta exceeds the
  // burn cost.
  const burnImageSide = Number.isFinite(priorWarmTokens) && priorWarmTokens > 0
    ? priorWarmTokens * (CACHE_CREATE_RATE - CACHE_READ_RATE)
    : 0;
  const burnTextSide = Number.isFinite(priorWarmImageTokens) && priorWarmImageTokens > 0
    ? priorWarmImageTokens * (CACHE_CREATE_RATE - CACHE_READ_RATE)
    : 0;
  return imageTokensCost_ + burnImageSide < textTokensEquivalent + burnTextSide;
}

/**
 * Horizon-aware variant of `isCompressionProfitable` for the
 * **history-collapse** call site only.
 *
 * The per-turn gate (above) compares cold image cost vs cold text cost.
 * That's the
[assistant]
Looked at src/core/history.ts; continuing with the change.

=== end of transcript ===
