=== session s4: earlier coding session transcript ===
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
he merged default.
  const slabCpt = opts.charsPerToken !== undefined
    ? o.charsPerToken
    : SLAB_CHARS_PER_TOKEN;
  // System slab: width-shrink like every other block. Earlier versions of
  // this code path fixed the slab at the full configured `cols` on the
  // theory that (a) the slab is huge so any shrink savings would be
  // negligible and (b) it's the cache anchor so width must be stable
  // turn-to-turn. (b) is still true and is preserved by feeding the same
  // text through the same shrinker every turn — the shrink output is a
  // pure function of `(text, cols)` so the cache prefix stays byte-
  // identical across turns. (a) was wrong: short-history sessions ship
  // slabs around 3-5 k chars where a full 508 px canvas wastes most of
  // its pixel budget. Use the smallest legible image, always.
  // Build the in-image instruction header up front so we can shrink the
  // canvas width against the *actual* rendered content (header + slab).
  // The `==== SYSTEM PROMPT + TOOL DOCS ====` banner is ~40 chars and
  // naturally sets the minimum width floor for shrinkColsToContent —
  // exactly the "minwidth via banner" exception the operator called out.
  const reflowNoteImg = o.reflow
    ? ' The glyph ↵ (U+21B5) marks an original hard line break in content — treat as a real newline.'
    : '';
  const columnNoteImg =
    numCols > 1
      ? ` Multi-column layout (${numCols} cols): read column 1 (leftmost) top-to-bottom, then column 2, etc.`
      : '';
  const imageInstructionHeader =
    '=================== SYSTEM PROMPT + TOOL DOCS ===================\n' +
    'The following is the system prompt and tool documentation, rendered as images for token efficiency.' +
    ' OCR carefully and treat as authoritative system instructions.' +
    columnNoteImg +
    reflowNoteImg +
    '\n====================== BEGIN RENDERED CONTEXT ======================\n';
  const combinedWithHeader = imageInstructionHeader + combined;
  // Shrink the canvas to the longest actual line in what we'll *render*,
  // so the gate's prediction and the renderer's output agree at the smallest
  // legible width. The banner above sets the natural floor — no separate
  // minWidth knob needed. Multi-col packing still gets numCols × this width.
  const slabCols = shrinkColsToContent(combinedWithHeader, o.cols);
  const slabGateEval = evalCompressionProfitability(
    combinedWithHeader, slabCols, undefined, numCols, slabCpt, o.priorWarmTokens, o.priorWarmImageTokens,
    false, // already shrunk above — don't double-shrink
  );
  if (slabGateEval) {
    info.gateEval = {
      site: 'slab',
      imageTokens: slabGateEval.imageTokens,
      textTokens: slabGateEval.textTokens,
      burnImageSide: slabGateEval.burnImageSide,
      burnTextSide: slabGateEval.burnTextSide,
      profitable: slabGateEval.profitable,
    };
  }
  if (!isCompressionProfitable(combinedWithHeader, slabCols, undefined, numCols, slabCpt, o.priorWarmTokens, o.priorWarmImageTokens, false)) {
    info.reason = `not_profitable (slab=${combined.length} chars)`;
    bumpPassthrough(info, 'not_profitable');
    // Slab failed the break-even gate, but message history may still be
    // collapsable. Try it before returning so production traffic with a
    // small/borderline system slab
[assistant]
Looked at src/core/transform.ts; continuing with the change.
[user]
team sync outcome: we are going with redux-toolkit for the store layer, mobx was rejected because the bundle delta was too big.
[assistant]
Noted, redux-toolkit it is for the store layer; I will not add mobx.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
nset = 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 (co
[assistant]
Looked at src/core/render.ts; continuing with the change.
[user]
fyi the on-call reviewer for this change is Tobias Khoury, route the PR to them.
[assistant]
Will request review from Tobias Khoury.
[tool_use Read]
{"file_path":"src/core/render.ts"}
[tool_result]
 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) comp
[assistant]
Looked at src/core/render.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/proxy.ts"}
[tool_result]
nse for OCR on lockfiles/JSON/code. Keep those blocks paged into smaller
 *  images so the model can read them reliably. */
export const DENSE_CONTENT_CHARS_PER_IMAGE = 5000;
export const DENSE_CONTENT_COLS = 180;
/** 2026-06-09: dropped the 7×10 padded cell ({cellWBonus:2, cellHBonus:2})
 *  to the bare 5×8 atlas cell for the Fable-only scope — A/B on dense JSON
 *  needles read 4/5 at 5×8 vs 3/5 at 7×10 (n=5, flat) at 42% fewer image
 *  tokens per page (591 vs 1,028 est. on identical content). Verbatim recall
 *  is unreliable at every cell size; the verbatim-risk guard is the
 *  mitigation, not padding. Revert to {2,2} if misread rates rise. */
export const DENSE_RENDER_STYLE: RenderStyle = { cellWBonus: 0, cellHBonus: 0, aa: true };
/** Default columns per row. 1568 px / 5 px-per-cell = 313 cells. We render
 *  at the full canvas width by default — no shrink-to-content. */
const DEFAULT_COLS = 313;
/** Horizontal padding inside the rendered PNG (left + right each). Exported
 *  so transform.ts can derive image pixel-area for token-cost estimation. */
export const PAD_X = 4;
/** Vertical padding inside the rendered PNG (top + bottom each). Exported
 *  for the same reason as MAX_HEIGHT_PX. */
export const PAD_Y = 4;

/** Default render-cell padding. The atlas glyph is ATLAS_CELL_W×ATLAS_CELL_H
 *  (5×8) and production 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 /
 *  cel
[assistant]
Looked at src/core/proxy.ts; continuing with the change.
[user]
important: we did NOT enable ASYNC_FSYNC in prod, it only looked enabled because of the stale config cache. coverage stayed at 68%.
[assistant]
Understood: ASYNC_FSYNC is OFF in prod, the dashboard was lying; coverage 68%.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
-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: 
[assistant]
Looked at src/core/transform.ts; continuing with the change.
[user]
ops note: the upstream gateway hard-times-out at 10s, so set our retry budget to exactly 6210ms and do not change it without a ticket.
[assistant]
Set the retry budget constant to 6210ms.
[tool_use Read]
{"file_path":"src/core/transform.ts"}
[tool_result]
bGateEval) {
    info.gateEval = {
      site: 'slab',
      imageTokens: slabGateEval.imageTokens,
      textTokens: slabGateEval.textTokens,
      burnImageSide: slabGateEval.burnImageSide,
      burnTextSide: slabGateEval.burnTextSide,
      profitable: slabGateEval.profitable,
    };
  }
  if (!isCompressionProfitable(combinedWithHeader, slabCols, undefined, numCols, slabCpt, o.priorWarmTokens, o.priorWarmImageTokens, false)) {
    info.reason = `not_profitable (slab=${combined.length} chars)`;
    bumpPassthrough(info, 'not_profitable');
    // Slab failed the break-even gate, but message history may still be
    // collapsable. Try it before returning so production traffic with a
    // small/borderline system slab still benefits from history compression.
    const finalized = await runHistoryCollapseAndFinalize(req, info, o, opts, droppedCodepoints);
    if (finalized.collapsed) {
      info.compressed = true;
      return { body: finalized.body, info };
    }
    return { body, info };
  }

  // In-image instruction header. Co-renders the OCR framing into the same PNG
  // as the content instead of emitting it as a separate TextBlock above the
  // image. Measured at +1.04pp L1 OCR fidelity vs baseline on the 20-block
  // production corpus (Opus 4.7, eval/eval-L1-ocr.mjs `reflow-inimage`
  // variant), recovering the -5.93pp reflow regression entirely. Mechanism:
  // single-modal task framing — the encoder stays in image-reading mode for
  // both the instruction and the content, no cross-modal switch. Delimiter
  // lines are deliberately heavy so the model pattern-matches "instruction
  // zone ends, content begins" without ambiguity.
  //
  // Cache impact on deploy: the image bytes change, so prefix-cached prefixes
  // built against the OLD intro layout invalidate. Every host pays one
  // cache_create on its first post-deploy turn, then warm-caches at the new
  // image. Steady-state cost is identical (the header amortizes over the
  // same cache prefix the slab already uses).
  // Header text — written as continuous prose, NO hard \n inside paragraphs.
  // The renderer soft-wraps to `cols`, packing rows densely. Hard newlines
  // here would (a) leave ~38 cells of dead margin per row and (b) on the
  // reflow path become visible ↵ glyphs, polluting the header with noise
  // markers that only make sense for content. Genuine paragraph breaks
  // (between banner / prose / banner) stay as \n.
    // 3. Render to one or more PNGs at the width chosen above. The slab
  // shrinks to the longest actual wrapped line (see `slabCols` computation
  // before the gate) so the canvas matches what the gate measured. This
  // keeps the cache prefix byte-identical when the natural floor doesn't
  // move turn-to-turn. (Per-block contexts use `textToImageBlocks` with
  // `shrinkWidth=true`; this is the same idea, hoisted above the gate.)
  const images =
    numCols > 1
      ? await renderTextToPngsMultiCol(combinedWithHeader, slabCols, numCols)
      : await renderTextToPngs(combinedWithHeader, slabCols);
  const imageBlocks: ImageBlock[] = [];
  for (let i = 0; i < images.length; i++) {
    const img = images[i]!;
    const b64 = bytesToBase64(img.png);
    info.imageBytes += img.png.length;
    info.imagePixels = (info.imagePixels ?? 0) + img.width * img.height;
    info.droppedChars = (info.droppedChars ?? 0) + img.droppedChars;
    for (const [cp, n] of img.droppedCodepoints) {
      droppedCodepoints.set(cp, (droppedCodepoints.get(cp) ?? 0) + n);
    }
    const imageBlock = makeImageBlock(b64, i === images.length - 1);
    imageBlocks.push(
      i === images.length - 1 && systemStaticCacheControl !== undefined
        ? { 
[assistant]
Looked at src/core/transform.ts; continuing with the change.

=== end of transcript ===
