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## The report
A user's model called compressed subagent output "too garbled to use"
and burned CCR retrievals to reconstruct it — **not** because it needed
more context. One retrieval returned nothing but the Claude Code harness
sanitizer banner, reported as `original_item_count: 33,
compressed_item_count: 25`.
Root-cause chain (verified by reproduction): the harness prepends a
bracket-delimited banner (`[harness: ... you.]` — exactly 33
whitespace-delimited words) and neutralizes `<` → `<\`. Headroom's
mixed-content splitter typed the banner as JSON (bracket balance, no
validation) → SmartCrusher couldn't parse it → the fallback chain fed it
to lossy Kompress → Kompress word-dropped the banner 33→25 and stored it
behind a retrieval hash. Meanwhile tabular sections rendered as
quote-wrapped JSON-string blobs with `\n` as two-character escapes, and
`ensure_ascii=True` boundaries turned the output's unicode (`→ └ ✓`)
into `\uXXXX` soup. The model reasonably concluded the output was
garbled.
## Fixes
1. **`split_into_sections` validates JSON before typing a block
`JSON_ARRAY`** — same validation its own mixed-content gate
(`_has_valid_json_block_with_text`) has always used. Tag-protection
placeholders, which self-isolated only by accident of that bug
(`{{HEADROOM_TAG_N}}` bracket-balances), are now isolated explicitly via
a new `isolate=` parameter fed by the router; contiguous prose fragments
re-coalesce so the `\n\n` reassembly stops doubling newlines in
uncompressed prose.
2. **Kompress gets a real floor: `min_input_words = 64`**
(config-tunable, clamped at the historical 10), applied on the
in-process, batch, apply, and remote paths. Below it, lossy
word-dropping is a net loss — the retrieval marker alone is ~20 words —
and short blocks are disproportionately instruction-like.
3. **The mixed path unwraps SmartCrusher's whole-array CSV render** when
it comes back as a bare JSON string, splicing raw readable lines into
the text instead of a quoted escape blob.
4. **`ensure_ascii=False` at model-visible boundaries**: MCP
retrieve/stats responses and the audit-safe splice reserialization
(which now also matches serde_json's non-escaping behavior).
5. **Kompress honesty**: the marker says `N words compressed to M`
(shared `ccr_retrieval_marker` helper, unit-tested), and
`store_kompress_in_ccr` no longer writes word counts into the store's
*item count* fields — token counts already carry the size story.
The upstream trigger (the harness's `<` → `<\` neutralization corrupting
JSON semantics) is not Headroom's to fix, but with #1 and #2 the banner
now passes through byte-intact and nothing lossy touches it.
## Testing
- New `tests/test_garbled_compression_fixes.py` (12 tests) pins every
fix, including an end-to-end router pass over a reconstructed
harness-sanitized fixture asserting the banner survives byte-identical
and no `\uXXXX` appears.
- Existing small-fixture kompress/router tests updated to set
`min_input_words=10` explicitly (they test other mechanics; fixtures sit
under the new production floor by design).
- Affected sweep (`-k "compress or ccr or crusher or router or mixed or
kompress or hermes"`, ~2.9k tests): green apart from order-dependent
flakes that shift identity between runs (deepseek tokenizer `AutoConfig`
import, hermes/proxy-ccr) — each passes standalone and in direct
combination with the new tests; the full CI shards are the authoritative
check.
- ruff 0.16.3 `check` + `format --check` clean.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
https://claude.ai/code/session_01EWKCmcH47hvvoQ35wftXhE
---------
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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|---|---|---|
| .. | ||
| __init__.py | ||
| test_code_compressor.py | ||
| test_code_compressor_cjk.py | ||
| test_content_router.py | ||
| test_content_router_ccr_retrieve_exemption.py | ||
| test_detect_fallback_1123.py | ||
| test_diff_compressor.py | ||
| test_diff_compressor_rust_parity.py | ||
| test_html_extractor.py | ||
| test_kompress_compressor.py | ||
| test_kompress_deadline.py | ||
| test_kompress_remote.py | ||
| test_kompress_size_gate.py | ||
| test_ort_dylib.py | ||
| test_pipeline_waste_signal_limit.py | ||
| test_read_lifecycle.py | ||
| test_smart_crusher_attribution.py | ||
| test_smart_crusher_audit_safe.py | ||
| test_smart_crusher_bugs.py | ||
| test_smart_crusher_ccr_retrieve_exemption.py | ||
| test_smart_crusher_ccr_roundtrip.py | ||
| test_smart_crusher_lossless_default.py | ||
| test_smart_crusher_rust_parity.py | ||
| test_tag_protector.py | ||
| test_text_crusher.py | ||
| test_text_crusher_cjk_eval.py | ||
| test_text_crusher_parity.py | ||
| test_text_crusher_routing.py | ||
| test_tree_sitter_thread_safety.py | ||