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## Description
`/v1/compress` does no format conversion — callers send whichever wire
shape they already use — but the pipeline pinned **one provider's token
counter for the whole route**.
`OpenAITokenCounter.count_message` walks list content for `text` and
`image_url` only and has **no else branch**, so Anthropic content blocks
contributed literally zero. A 599-token `tool_result` scored 8. A
request that really removed 235 characters reported `tokens_saved: 0` —
so a caller gating on `tokens_saved > 0` concludes compression is broken
while it is working.
Prompted by a Kong integration question ("do you support the Anthropic
native format?"). The answer is that we already did — we just reported
zeros for it, and the docs said otherwise.
Closes #
## Type of Change
- [x] Bug fix (non-breaking change that fixes an issue)
- [x] Documentation update
## Changes Made
### Tokenizer resolution (no hardcoded lists)
Build the derived pipelines with `provider=None` so `TransformPipeline`
resolves the tokenizer from the **per-model registry**. Every registry
tokenizer derives from `BaseTokenizer`, whose `_count_content_parts`
ends in a serialize-and-count catch-all, which means:
- No block type counts as zero, and there is **no per-provider
block-type list to keep in sync**. An enumerated set was the first thing
I tried and it already missed `mcp_tool_result`,
`web_search_tool_result`, `document`, and `thinking`.
- Gemini / Mistral / DeepSeek / Kimi stop defaulting to a tiktoken count
when the registry already has a calibrated counter for them.
- Gateway aliases matching no vendor pattern still count correctly.
`mode="ccr"` now runs a derived pipeline too, for the same reason —
sharing `openai_pipeline` pinned its provider. Costs that mode its own
cold compression cache; correct metrics win.
### Tokenizer selection stays separate from context-limit resolution
Deliberately not welded together. `model_limit` feeds `context_pressure
-> min_ratio`, so letting a tokenizer decision pick the limit table
changes compression aggressiveness: `gpt-4-32k` answered by the
Anthropic table is **8,192 instead of 32,768**, a 4× under-estimate.
`test_tokenizer_choice_does_not_move_the_context_limit` pins the
independence.
### Docs, rewritten from the code
- **`proxy.mdx`** — the loopback-only default and **404-not-403**
behavior, previously undocumented *anywhere* in `docs/` despite shipping
in #2458 explicitly for gateway sidecars;
`HEADROOM_COMPRESS_ALLOW_REMOTE`; all four request fields; the whole
`config` object including every `mode` value and `frozen_message_count`;
`transforms_summary`; the 400/401/404/503 contract; and the timeout
fail-open shape (`compression_skipped` / `skip_reason`).
- **Corrected "never calls an LLM"** — accurate about *generative*
provider requests, misleading for a sidecar operator. Kompress (a
ModernBERT **encoder**, classification not generation) and Magika run
**in-process**, and `HEADROOM_KOMPRESS_ENDPOINT` offloads inference over
HTTP — **real egress**. Now stated explicitly, with
`HEADROOM_DISABLE_KOMPRESS=1` as the structural-only option.
- **Both wire formats documented as accepted**, and removed
`anthropic-sdk.mdx`'s claim that OpenAI format is "the compression
engine's native format" — the exact misconception that prompted this
work. The SDK's conversion is now framed as an SDK choice, not an API
requirement.
- **`litellm.mdx`** had no mention of the endpoint at all, despite the
code naming LiteLLM's guardrail as its primary consumer. Added the HTTP
deployment path, the `HEADROOM_COMPRESS_ALLOW_REMOTE` requirement, and
why to leave `config.mode` unset.
- **`index.mdx`** printed `compressionRatio * 100` labelled "Saved …%",
so a 77% saving displayed as **23%**. `api-reference.mdx` already
defined it correctly, so the docs contradicted each other.
- `openai-sdk.mdx`, `wiki/proxy.md`, `wiki/typescript-sdk.md` — same
corrections; dropped "any HTTP client", "Cloud", and a CacheAligner
claim (it is detector-only).
## Testing
- [x] Unit tests pass (`pytest`)
- [x] Linting passes (`ruff check .`)
- [x] Type checking passes (`mypy headroom`)
- [x] New tests added for new functionality
- [x] Manual testing performed
### Test Output
```text
$ .venv/bin/ruff check headroom/ tests/ --exclude headroom/dashboard/templates
All checks passed!
$ .venv/bin/mypy headroom/
Success: no issues found in 511 source files
$ python -m pytest tests/test_compress_route_tokenizer_by_model.py \
tests/test_proxy_compress_endpoint.py tests/test_compress_api.py \
tests/test_platform_stabilization_functional.py tests/test_proxy_eager_preload_bind.py -q
99 passed, 2 warnings in 47.15s
```
Broader sweep (`-k "compress or litellm or gateway or guardrail"`):
**1625 passed, 4 failed** — all 4 pre-existing, verified by stashing
this diff and re-running on clean `main` (2 strands hook tests, 1 codex
WS semaphore-tail timing test, 1 unrelated local WIP test).
## Real Behavior Proof
- **Environment:** macOS 26.4 arm64, Python 3.12.6, repo `.venv`, branch
rebased on `upstream/main`.
**(1) Before → after, same request** (60-line grep payload in an
Anthropic `tool_result`):
| model | before | after |
| --- | --- | --- |
| `claude-sonnet-4-6` | `before=28 saved=0` | `before=1223 saved=58` |
| `bedrock/anthropic.claude-3-5-sonnet` | `saved=0` | `before=1037
saved=59` |
| `my-gateway/big-model` (alias) | `saved=0` | `before=1037 saved=59` |
| `gemini-2.5-pro` | `saved=0` | `before=1036 saved=59` |
| `gpt-4o` + OpenAI shape | `before=1225 saved=58` | `before=1225
saved=58` (unchanged) |
All three `config.mode` values verified for each. Response shape
preserved: `type=tool_result`, `tool_use_id` intact.
**(2) Counter-level root cause**, 6.8 KB body, `count_message()`:
```text
OpenAITokenCounter string-content -> 1406 tool_result block -> 5
registry (BaseTokenizer) claude tool_result=408 thinking=418 mcp_tool_result=421
web_search_tool_result=421 document=422
```
**(3) Every documented behavior asserted against the running app** — 13
checks, all PASS: 400s for missing `messages`/`model`, invalid
`config.mode`, and all four invalid `frozen_message_count` forms; 200
for valid ones; non-dict `config` ignored; bypass and empty-messages
omit `transforms_summary`; success returns exactly the 8 documented
keys.
- **Not tested:** the docs site was not built (`docs/node_modules`
absent) — MDX was checked for balanced `<Callout>` tags only, so a
reviewer with the site running should eyeball rendering. No live
gateway/Kong request; verification is via `TestClient` against the real
ASGI app.
- **Note:** `HEADROOM_DISABLE_KOMPRESS` is read into `ProxyConfig` at
`server.py:4919` and by the CLI, not by `create_app(ProxyConfig(...))`
directly — I confirmed `disable_kompress=True` does reach the derived
pipeline.
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [x] I did **not** edit `CHANGELOG.md`
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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| .. | ||
| overrides | ||
| plans | ||
| screenshots | ||
| stylesheets | ||
| agno.md | ||
| api.md | ||
| ARCHITECTURE.md | ||
| benchmarks.md | ||
| ccr.md | ||
| cli.md | ||
| compression.md | ||
| configuration.md | ||
| docker-install.md | ||
| errors.md | ||
| filesystem-contract.md | ||
| getting-started.md | ||
| image-compression.md | ||
| index.md | ||
| integration-guide.md | ||
| langchain.md | ||
| LATENCY_BENCHMARKS.md | ||
| learn.md | ||
| LIMITATIONS.md | ||
| macos-deployment.md | ||
| mcp.md | ||
| memory.md | ||
| metrics.md | ||
| network-diff-capture.md | ||
| persistent-installs.md | ||
| proxy.md | ||
| quickstart.md | ||
| sdk.md | ||
| shared-context.md | ||
| strands.md | ||
| text-compression.md | ||
| transforms.md | ||
| troubleshooting.md | ||
| typescript-sdk.md | ||
| vertex.md | ||