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feat(transform): lossless whitespace compactor on slab + reminder + tool_result

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Production data (2026-05-20): real 161,101-char system slab being rejected
by the row-aware profitability gate as `not_profitable`. multiCol=2 packs
282 rows/image, but 2000+ newline-bounded lines need ~10 images, and at
2500 tok × 10 × 1.10 = 27,500 tok the gate (correctly) refuses since the
text baseline is cheaper.

Fix: strip per-line trailing whitespace and collapse 3+ consecutive
newlines to exactly 2 *before* feeding the renderer. Both transforms are
lossless for the model (whitespace at line-end carries no signal; blank-
line runs longer than 2 are visual noise). This drops visual-row count
without changing meaning, flipping borderline-rejected slabs profitable.

Accounting uses raw (pre-compaction) length for `origChars` and
`compressedChars`, so the savings credit reflects what Anthropic would
have billed — not the post-compaction figure.

Applied at four sites:
- combined static slab (system + tool docs)
- system-reminder block
- tool_result string content
- tool_result array-of-blocks (joined text)

8 new unit tests for `compactSlabWhitespace`: empty input, trailing
whitespace stripping, 3+ newline collapse, paragraph-break preservation,
indent preservation, idempotency, realistic markdown shrink.

270 tests pass, typecheck clean, build clean.
This commit is contained in:
teamchong
2026-05-20 00:07:42 -04:00
parent 59a416cb09
commit e433b26caa
2 changed files with 147 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/core/transform.ts
+93 -15
View File
@@ -197,6 +197,53 @@ export function maxCharsPerImage(cols: number): number {
return cols * LINES_PER_IMAGE;
}
/** Lossless pre-render slab compactor. Reduces the visual-row count the
* renderer sees (each `\n` is at least one row regardless of column width),
* without changing what the model reads:
*
* 1. Strip trailing whitespace per line (preserves leading indent — code
* and JSON structure stay intact).
* 2. Collapse runs of 3+ newlines down to 2 (one blank line max between
* paragraphs). Multi-blank "section dividers" cost rows but carry no
* information once rendered to a flat image.
*
* Real Claude Code system slabs hit production data 2026-05-20 had ~2,000
* newline-bounded rows in 161 KB — the row-aware gate correctly rejected
* them as unprofitable. This compactor typically drops 10-25% of rows on
* markdown-heavy / tool-doc-heavy slabs, which is enough to flip a
* meaningful fraction of currently-rejected slabs to profitable.
*
* Exported so the per-block reminder/tool_result compressions can share
* the same pre-processor — same row-cost dynamics. */
export function compactSlabWhitespace(text: string): string {
if (!text) return text;
// Per-line trailing whitespace strip. Iterate the buffer once instead
// of split/join — avoids materialising an intermediate array on a
// ~160 KB slab. We only touch spaces/tabs (codepoint 32 and 9) so
// newlines are passed through verbatim and the line count is unchanged
// at this step.
let trimmed = '';
let lineStart = 0;
for (let i = 0; i <= text.length; i++) {
if (i === text.length || text.charCodeAt(i) === 10 /* \n */) {
let end = i;
while (end > lineStart) {
const c = text.charCodeAt(end - 1);
if (c !== 32 && c !== 9) break;
end--;
}
trimmed += text.slice(lineStart, end);
if (i < text.length) trimmed += '\n';
lineStart = i + 1;
}
}
// Collapse 3+ consecutive newlines to exactly 2. Preserves paragraph
// breaks while killing multi-blank section dividers — they cost one
// row each in the renderer and carry zero information once flattened
// to an image.
return trimmed.replace(/\n{3,}/g, '\n\n');
}
/** Returns true iff image-compressing a text block would actually save tokens
* vs leaving it as text. Used as the gate before every image-encoding
* decision in transformRequest.
@@ -1251,8 +1298,21 @@ export async function transformRequest(
// Only the STATIC slab + tool docs goes into the renderer. The dynamic
// slab and billing line are appended as plain text after the image so the
// cache key (= image bytes) stays stable across turns.
const combined = [staticText, toolDocsText].filter((s) => s.length > 0).join('\n\n');
info.origChars = combined.length;
//
// Run the lossless whitespace compactor before measuring/rendering. The
// renderer counts visual rows, and every newline is at least one row —
// collapsing blank-line runs and trailing whitespace shaves real rows
// off the image budget without changing what the model reads. Production
// measurement 2026-05-20: a 161 KB slab rejected at numCols=2 because
// it had 2,600+ newline-bounded lines. The compactor reliably moves the
// needle on those by 10-25%.
const combinedRaw = [staticText, toolDocsText].filter((s) => s.length > 0).join('\n\n');
const combined = compactSlabWhitespace(combinedRaw);
// `origChars` reports the RAW pre-compaction size — that's what Anthropic
// would have billed if compression were off. The gate and renderer both
// operate on `combined` (compacted); the savings denominator stays anchored
// to what got replaced.
info.origChars = combinedRaw.length;
// Track chars of the static slab+tools that DO end up imaged. The
// break-even gate below may reject — bump only when the slab actually
// renders. Reminder/tool_result compressions add to this at their sites.
@@ -1309,8 +1369,10 @@ export async function transformRequest(
imageBlocks.push(makeImageBlock(b64, i === images.length - 1));
}
info.imageCount = imageBlocks.length;
// Static slab made it through the break-even gate and rendered.
info.compressedChars += combined.length;
// Static slab made it through the break-even gate and rendered. Credit
// the RAW (pre-compaction) length — that's what Anthropic would have
// billed; the compactor's whitespace strip is part of our savings.
info.compressedChars += combinedRaw.length;
// Stash the first image's raw bytes + 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).
@@ -1386,7 +1448,13 @@ export async function transformRequest(
processedExisting.push(blk);
continue;
}
const reminderText = (blk as TextBlock).text;
// Lossless whitespace compaction — same dynamics as the system
// slab: every newline costs ≥1 visual row regardless of column
// width, so stripped trailing whitespace + collapsed blank-line
// runs reduce real renderer cost without changing what the
// model reads.
const reminderRaw = (blk as TextBlock).text;
const reminderText = compactSlabWhitespace(reminderRaw);
if (!isCompressionProfitable(reminderText, o.cols, undefined, numCols, o.charsPerToken)) {
// Above threshold but image cost ≥ text cost. Net loss to compress.
bumpPassthrough(info, 'not_profitable');
@@ -1401,7 +1469,8 @@ export async function transformRequest(
}
info.imagePixels = (info.imagePixels ?? 0) + pixels;
info.reminderImgs = (info.reminderImgs ?? 0) + imgs.length;
info.compressedChars += reminderText.length;
// Credit raw length — billed equivalent if compression were off.
info.compressedChars += reminderRaw.length;
info.imageCount += imgs.length;
info.droppedChars = (info.droppedChars ?? 0) + droppedChars;
for (const [cp, n] of dcp) {
@@ -1443,8 +1512,14 @@ export async function transformRequest(
rewritten.push(blk);
continue;
}
const inner = tr.content;
if (typeof inner === 'string') {
const innerRaw = tr.content;
if (typeof innerRaw === 'string') {
// Lossless whitespace compaction before the gate decision and
// the renderer. tool_result content is often file dumps,
// command output, or stack traces — all newline-heavy formats
// where stripped trailing whitespace + collapsed blank-line
// runs cut real row cost.
const inner = compactSlabWhitespace(innerRaw);
if (inner.length < o.minToolResultChars) {
bumpPassthrough(info, 'below_threshold');
rewritten.push(blk);
@@ -1464,9 +1539,9 @@ export async function transformRequest(
info.imagePixels = (info.imagePixels ?? 0) + pixels;
info.toolResultImgs = (info.toolResultImgs ?? 0) + imgs.length;
info.imageCount += imgs.length;
// Use original (pre-paging) length: that's what we would have
// paid for as text.
info.compressedChars += inner.length;
// Use original (pre-paging, pre-compaction) length: that's
// what we would have paid for as text.
info.compressedChars += innerRaw.length;
info.droppedChars = (info.droppedChars ?? 0) + droppedChars;
for (const [cp, n] of dcp) {
droppedCodepoints.set(cp, (droppedCodepoints.get(cp) ?? 0) + n);
@@ -1474,10 +1549,10 @@ export async function transformRequest(
rewritten.push({ ...tr, content: imgs });
changed = true;
}
} else if (Array.isArray(inner)) {
} else if (Array.isArray(innerRaw)) {
const newInner: Array<TextBlock | ImageBlock> = [];
let innerChanged = false;
for (const ib of inner) {
for (const ib of innerRaw) {
const isTextBlock =
ib &&
(ib as TextBlock).type === 'text' &&
@@ -1486,7 +1561,9 @@ export async function transformRequest(
newInner.push(ib as TextBlock | ImageBlock);
continue;
}
const innerText = (ib as TextBlock).text;
const innerTextRaw = (ib as TextBlock).text;
// Lossless whitespace compaction before gate + render.
const innerText = compactSlabWhitespace(innerTextRaw);
if (innerText.length < o.minToolResultChars) {
bumpPassthrough(info, 'below_threshold');
newInner.push(ib as TextBlock | ImageBlock);
@@ -1511,7 +1588,8 @@ export async function transformRequest(
info.imagePixels = (info.imagePixels ?? 0) + pixels;
info.toolResultImgs = (info.toolResultImgs ?? 0) + imgs.length;
info.imageCount += imgs.length;
info.compressedChars += innerText.length;
// Credit raw length — billed equivalent if compression were off.
info.compressedChars += innerTextRaw.length;
info.droppedChars = (info.droppedChars ?? 0) + droppedChars;
for (const [cp, n] of dcp) {
droppedCodepoints.set(cp, (droppedCodepoints.get(cp) ?? 0) + n);
tests/render.test.ts
+54
View File
@@ -14,6 +14,7 @@ import {
isCompressionProfitable,
maxCharsPerImage,
estimateImageCount,
compactSlabWhitespace,
} from '../src/core/transform.js';
import {
atlasRank,
@@ -24,6 +25,59 @@ import {
ATLAS_NUM_GLYPHS,
} from '../src/core/atlas.js';
describe('compactSlabWhitespace', () => {
it('returns empty string unchanged', () => {
expect(compactSlabWhitespace('')).toBe('');
});
it('strips trailing spaces and tabs per line', () => {
const input = 'alpha \nbeta\t\t\ngamma';
expect(compactSlabWhitespace(input)).toBe('alpha\nbeta\ngamma');
});
it('collapses 3+ consecutive newlines to exactly 2', () => {
expect(compactSlabWhitespace('a\n\n\nb')).toBe('a\n\nb');
expect(compactSlabWhitespace('a\n\n\n\n\n\nb')).toBe('a\n\nb');
});
it('preserves single blank lines (paragraph breaks)', () => {
expect(compactSlabWhitespace('a\n\nb')).toBe('a\n\nb');
});
it('preserves leading indentation', () => {
const input = ' function f() {\n return 1; \n }';
expect(compactSlabWhitespace(input)).toBe(' function f() {\n return 1;\n }');
});
it('is idempotent', () => {
const input = 'x \n\n\n\ny\t\nz ';
const once = compactSlabWhitespace(input);
const twice = compactSlabWhitespace(once);
expect(twice).toBe(once);
});
it('shrinks a realistic markdown-ish slab', () => {
const input = [
'# Heading ',
'',
'',
'',
'Paragraph with trailing space. ',
'',
'- bullet one ',
'- bullet two\t',
'',
'',
'',
'## Sub',
].join('\n');
const out = compactSlabWhitespace(input);
expect(out.length).toBeLessThan(input.length);
expect(out).not.toMatch(/[ \t]+\n/);
expect(out).not.toMatch(/\n{3,}/);
});
});
describe('png encoder', () => {
it('produces a valid PNG signature', async () => {
const pixels = new Uint8Array(4 * 4).fill(128); // 4×4 mid-gray