refactor(internal): extract body-cap module out of client.py

Extracts the max_response_body_bytes body-capping subsystem and the two
httpx2-exception-mapper context managers out of client.py into
_internal/body_cap.py (new) and _internal/exception_mapping.py — pure
move, no behavior change. Fixes a doc-location claim in
architecture/errors.md/client.md that this move made stale.

Design: planning/changes/2026-07-13.01-body-cap-module-extraction.md

Author: lesnik512

architecture/client.md

@@ -4,7 +4,7 @@
 
 ## The internal terminal
 
-The bottom of the middleware chain (the "terminal") is internal. It calls `self._httpx2_client.send(request)`, maps `httpx2` errors to `httpware` errors, and raises a `StatusError` subclass on 4xx/5xx. The error-mapping table (what `httpx2` exception maps to which `httpware` exception) lives at the terminal in `src/httpware/client.py`; status-keyed exceptions are looked up via the `STATUS_TO_EXCEPTION` table in `src/httpware/errors.py`. The same terminal lifecycle holds in both worlds: `Client.send` / `AsyncClient.send` enter the middleware chain first, and it is the internal terminal — `Client._terminal` / `AsyncClient._terminal` — that calls `httpx2.Client.send` / `httpx2.AsyncClient.send`.
+The bottom of the middleware chain (the "terminal") is internal. It calls `self._httpx2_client.send(request)`, maps `httpx2` errors to `httpware` errors, and raises a `StatusError` subclass on 4xx/5xx. The error-mapping table (what `httpx2` exception maps to which `httpware` exception) lives in `src/httpware/_internal/exception_mapping.py` and fires at the terminal in `src/httpware/client.py`; status-keyed exceptions are looked up via the `STATUS_TO_EXCEPTION` table in `src/httpware/errors.py`. The same terminal lifecycle holds in both worlds: `Client.send` / `AsyncClient.send` enter the middleware chain first, and it is the internal terminal — `Client._terminal` / `AsyncClient._terminal` — that calls `httpx2.Client.send` / `httpx2.AsyncClient.send`.
 
 ## Sync/async parity
 

architecture/errors.md

@@ -10,7 +10,7 @@ exc.response.request.url               # URL of the failed request
 
 `__repr__` and the `str()` summary redact URL userinfo (`user:pass@`) and mask the values of known-sensitive query and fragment parameters (e.g. `token`, `api_key`, `secret`) to avoid leaking credentials in tracebacks.
 
-The error-mapping table (what `httpx2` exception maps to which `httpware` exception) lives at the terminal in `src/httpware/client.py`. Status-keyed exceptions are looked up via the `STATUS_TO_EXCEPTION` table in `src/httpware/errors.py`. Unknown 4xx falls back to `ClientStatusError`; unknown 5xx falls back to `ServerStatusError`.
+The error-mapping table (what `httpx2` exception maps to which `httpware` exception) lives in `src/httpware/_internal/exception_mapping.py` and fires at the terminal in `src/httpware/client.py`. Status-keyed exceptions are looked up via the `STATUS_TO_EXCEPTION` table in `src/httpware/errors.py`. Unknown 4xx falls back to `ClientStatusError`; unknown 5xx falls back to `ServerStatusError`.
 
 `TimeoutError` inherits from both `httpware.ClientError` and `builtins.TimeoutError` so `except builtins.TimeoutError` (the form `asyncio.wait_for` uses) also catches httpware-raised timeouts.
 

architecture/overview.md

@@ -35,8 +35,9 @@ src/httpware/
 │       └── _backoff.py    # full-jitter helper (shared)
 ├── decoders/              # shared (ResponseDecoder + adapters)
 └── _internal/
-    ├── exception_mapping.py  # map_httpx2_exception (shared)
-    ├── import_checker.py     # is_*_installed flags
-    ├── observability.py      # _emit_event
-    └── status.py             # _raise_on_status_error, _is_streaming_body_*, STREAMING_BODY_MARKER
+    ├── body_cap.py            # max_response_body_bytes: validate, read-capped (sync+async)
+    ├── exception_mapping.py   # map_httpx2_exception + context-manager wrappers (shared)
+    ├── import_checker.py      # is_*_installed flags
+    ├── observability.py       # _emit_event
+    └── status.py              # _raise_on_status_error, _is_streaming_body_*, STREAMING_BODY_MARKER
 ```

planning/changes/2026-07-13.01-body-cap-module-extraction.md

@@ -0,0 +1,155 @@
+---
+summary: Extract the body-cap subsystem and the httpx2-exception-mapper context managers out of client.py into dedicated _internal/ modules.
+---
+
+# Design: Extract the body-cap subsystem into `_internal/body_cap.py`
+
+## Summary
+
+`client.py:38-212` holds ~180 lines of pure, self-contained code with zero
+`self`/`Client`/`AsyncClient` coupling: the `max_response_body_bytes`
+body-capping subsystem (`_validate_max_response_body_bytes`,
+`_parse_content_length`, `_CapExceeded`, `_accumulate_capped`,
+`_safe_extensions`, `_buffered_headers`, `_response_has_body`,
+`_read_capped`, `_read_capped_async`) and two httpx2-exception-mapper context
+managers (`_httpx2_exception_mapper`, `_httpx2_exception_mapper_sync`). This
+change moves the body-cap subsystem into a new `_internal/body_cap.py`, and
+folds the two context managers into the existing `_internal/exception_mapping.py`
+next to the `map_httpx2_exception` function they wrap. No behavior change.
+
+## Motivation
+
+- `client.py` is 2,154 lines, by far the largest module in the package.
+  Everything genuinely coupled to `Client`/`AsyncClient` (`_terminal`,
+  `_prepare_request`, `stream()`) has to stay there; ~200 lines of this file
+  currently don't.
+- The package already has a home for exactly this shape of code:
+  `_internal/status.py` holds `_raise_on_status_error` and the
+  streaming-body predicates, `_internal/exception_mapping.py` holds
+  `map_httpx2_exception` — both pure, self-contained, shared by both clients.
+  The body-cap subsystem and the exception-mapper context managers are the
+  same shape and never received the same treatment.
+- Same-day precedent: `2026-06-23.01-retry-policy-extraction.md` and
+  `2026-06-23.02-decoder-resolver-extraction.md` pulled comparable
+  self-contained logic out of their hosting files into dedicated modules.
+  `2026-06-23.03-response-body-cap.md` landed the body-cap subsystem directly
+  in `client.py` the same day and never got the follow-up move.
+- **Depth:** the body-cap subsystem's own tests (`tests/test_capped_read.py`,
+  `tests/test_capped_read_props.py`) already exercise it as a standalone
+  unit, importing the functions directly rather than through `Client`. The
+  seam already exists in the tests; the source hasn't caught up.
+- **Deletion test:** delete `_internal/body_cap.py` after this change and the
+  ~150 lines of cap-accumulation/header-rebuild logic reappear somewhere —
+  it's real, load-bearing complexity, not a pass-through. It earns the move.
+
+## Design
+
+### 1. `_internal/body_cap.py` — new module
+
+Moves verbatim (no logic change):
+
+- `_MAX_RESPONSE_BODY_BYTES_INVALID`, `_validate_max_response_body_bytes`
+- `_parse_content_length`
+- `_CapExceeded`, `_accumulate_capped`
+- `_safe_extensions`
+- `_WIRE_BODY_HEADERS`, `_BODILESS_STATUS`, `_buffered_headers`
+- `_response_has_body`
+- `_read_capped`, `_read_capped_async`
+
+Needs its own imports: `httpx2`, `HTTPStatus` (from `http`), `Mapping` (from
+`collections.abc`), and `ResponseTooLargeError` (from `httpware.errors`) —
+all currently imported by `client.py` for this code's sake and dropped from
+`client.py`'s import block once it moves (`Mapping` and
+`ResponseTooLargeError` are used nowhere else in `client.py`; `HTTPStatus`
+stays imported in `client.py` because `stream()` uses it independently at
+`client.py:1152` and `:2146`).
+
+`_build_default_decoders` (`client.py:172-190`) stays in `client.py`.
+`architecture/decoders.md` documents its location explicitly ("`decoders=None`
+resolves via `client.py:_build_default_decoders()`"); it is the same shape of
+pure, self-contained code but moving it isn't part of this change's motivation
+and would mean editing a Seam B contract that this change has no reason to
+touch.
+
+### 2. `_internal/exception_mapping.py` — gains two context managers
+
+`_httpx2_exception_mapper` (async) and `_httpx2_exception_mapper_sync` (sync)
+move in next to `map_httpx2_exception`, which they already wrap. Same
+rationale as body-cap — pure, self-contained, sibling concern already has a
+module — bundled into this change rather than a second near-identical PR.
+
+### 3. `client.py` shrinks to three imported names
+
+Only `_validate_max_response_body_bytes` (called once per `__init__`),
+`_read_capped`, and `_read_capped_async` (called from `_terminal` and
+`stream()`, both worlds) are actually referenced from inside `Client`/
+`AsyncClient`. Every other moved name (`_parse_content_length`,
+`_CapExceeded`, `_accumulate_capped`, `_safe_extensions`, `_buffered_headers`,
+`_response_has_body`) is internal to `body_cap.py` and never imported by
+`client.py`. `_httpx2_exception_mapper`/`_httpx2_exception_mapper_sync` are
+imported by name, same call sites as today (`client.py:283`, `:1151`,
+`:1255`, `:2145`).
+
+```python
+from httpware._internal.body_cap import _read_capped, _read_capped_async, _validate_max_response_body_bytes
+from httpware._internal.exception_mapping import _httpx2_exception_mapper, _httpx2_exception_mapper_sync, map_httpx2_exception
+```
+
+Nine functions/one class collapse behind a three-name import in `client.py`
+for body-cap, plus the two context managers for exception mapping.
+
+### 4. `architecture/overview.md` — module-layout table
+
+Add a `body_cap.py` row under `_internal/`; update `exception_mapping.py`'s
+description to mention the context managers:
+
+```text
+└── _internal/
+    ├── body_cap.py            # max_response_body_bytes: validate, read-capped (sync+async)
+    ├── exception_mapping.py   # map_httpx2_exception + context-manager wrappers (shared)
+    ├── import_checker.py      # is_*_installed flags
+    ├── observability.py       # _emit_event
+    └── status.py              # _raise_on_status_error, _is_streaming_body_*, STREAMING_BODY_MARKER
+```
+
+## Non-goals
+
+- No behavior change. Cap validation, accumulation, header rebuild,
+  `ResponseTooLargeError` reasons, and exception-mapping order stay
+  byte-identical.
+- Not moving `_build_default_decoders` (see Design §1).
+- Not touching the public `max_response_body_bytes` parameter, its
+  validation error message, or `ResponseTooLargeError`'s shape.
+- Not addressing the larger `Client`/`AsyncClient` sync/async duplication
+  (the per-verb methods, `_prepare_request`, `_request_with_body`) — a
+  separate, much larger candidate surfaced in the same architecture review,
+  deliberately deferred pending its own design call.
+
+## Testing
+
+- **Parity net:** rename `tests/test_capped_read.py` →
+  `tests/test_body_cap.py` and `tests/test_capped_read_props.py` →
+  `tests/test_body_cap_props.py`, updating their imports from
+  `httpware.client` to `httpware._internal.body_cap`. All existing
+  assertions stay unchanged — byte-identical behavior is the bar.
+- Move `test_parse_content_length` (currently `tests/test_client_stream.py:446-447`,
+  testing a `body_cap.py` function directly rather than `stream()` behavior)
+  into `tests/test_body_cap.py`, updating its import.
+- No new tests — this is a pure move with an existing, adequate net
+  (`test_body_cap.py`, `test_body_cap_props.py`, `test_client_body_cap.py`
+  for cap wiring through the client, `test_error_mapping_terminal.py` for
+  exception-mapping-at-terminal behavior).
+- `just lint && just test` green; 100% coverage maintained.
+
+## Risk
+
+- **Import cycle** (unlikely × medium): `_internal/body_cap.py` imports
+  `httpware.errors.ResponseTooLargeError`. *Mitigation:* `_internal/status.py`
+  already imports from `httpware.errors` today with no cycle — same
+  direction, same precedent.
+- **Missed call site during the move** (unlikely × low): a stale import left
+  in `client.py`, or a name imported but now unused. *Mitigation:* `just
+  lint` catches unused imports; `just test` exercises every moved function
+  through its existing suite.
+- **Test-file rename loses git history readability** (certain × low):
+  `git mv` preserves blame across the rename; low impact either way.

src/httpware/_internal/body_cap.py

@@ -0,0 +1,146 @@
+"""Response-body cap enforcement: validate, read-capped (sync + async)."""
+
+import typing
+from collections.abc import Mapping
+from http import HTTPStatus
+
+import httpx2
+
+from httpware.errors import ResponseTooLargeError
+
+
+_MAX_RESPONSE_BODY_BYTES_INVALID = "max_response_body_bytes must be >= 1"
+
+
+def _validate_max_response_body_bytes(cap: int | None) -> None:
+    """Reject a non-None cap below 1. None means unbounded (the default)."""
+    if cap is not None and cap < 1:
+        raise ValueError(_MAX_RESPONSE_BODY_BYTES_INVALID)
+
+
+def _parse_content_length(raw: str | None) -> int | None:
+    """Return a non-negative int Content-Length, or None for missing/garbage. Never raises."""
+    if raw is None:
+        return None
+    try:
+        value = int(raw)
+    except ValueError:
+        return None
+    return value if value >= 0 else None
+
+
+class _CapExceeded(Exception):  # noqa: N818 — internal control-flow signal, not a user-facing error
+    """Internal signal: decoded bytes crossed the cap mid-read. Carries bytes read so far."""
+
+    def __init__(self, *, read: int) -> None:
+        self.read = read
+        super().__init__(f"decoded body exceeded cap after {read} bytes")
+
+
+def _accumulate_capped(chunks: typing.Iterable[bytes], cap: int) -> bytes:
+    """Concatenate `chunks`, raising `_CapExceeded` the moment the running total exceeds `cap`.
+
+    Counts decoded bytes (the in-memory footprint). Grown in a single bytearray
+    so there is no transient list-plus-join double allocation.
+    """
+    buf = bytearray()
+    for chunk in chunks:
+        buf += chunk
+        if len(buf) > cap:
+            raise _CapExceeded(read=len(buf))
+    return bytes(buf)
+
+
+def _safe_extensions(extensions: Mapping[str, typing.Any]) -> dict[str, typing.Any]:
+    """Copy response extensions, dropping the now-stale `network_stream`.
+
+    The rebuilt buffered Response never touches its network stream, so carrying a
+    consumed/closed one wholesale is sloppy. `http_version`/`reason_phrase` and
+    any other keys are preserved.
+    """
+    return {key: value for key, value in extensions.items() if key != "network_stream"}
+
+
+# Headers describing the wire encoding of the body. The accumulator yields the
+# DECODED body, so these no longer apply; httpx2 recomputes content-length from
+# the buffered content. Carrying content-encoding forward makes httpx2 try to
+# re-decode already-decoded bytes and raise.
+_WIRE_BODY_HEADERS = ("content-encoding", "content-length", "transfer-encoding")
+_BODILESS_STATUS = frozenset({HTTPStatus.NO_CONTENT, HTTPStatus.NOT_MODIFIED})  # 204, 304
+
+
+def _buffered_headers(headers: httpx2.Headers) -> httpx2.Headers:
+    """Copy `headers`, stripping wire-encoding headers stale after decoding+buffering."""
+    out = httpx2.Headers(headers)
+    for name in _WIRE_BODY_HEADERS:
+        if name in out:
+            del out[name]
+    return out
+
+
+def _response_has_body(method: str, status_code: int) -> bool:
+    """Whether a response carries a message body (RFC 9110 §6.4.1).
+
+    HEAD responses and 204/304 never have a body regardless of a declared
+    Content-Length, so they must never trip the cap.
+    """
+    return method.upper() != "HEAD" and status_code not in _BODILESS_STATUS
+
+
+def _read_capped(response: httpx2.Response, cap: int, request: httpx2.Request) -> httpx2.Response:
+    """Buffer a streaming sync `response` under `cap` decoded bytes; return a buffered Response.
+
+    Raises `ResponseTooLargeError` (reason="declared") if the declared
+    Content-Length already exceeds `cap` — before any byte is read — and
+    (reason="streamed") if the decoded body crosses `cap` mid-read. Does not
+    close `response`; the caller owns the stream lifecycle.
+    """
+    if not _response_has_body(request.method, response.status_code):
+        response.read()  # empty body; preserve the original response (and its headers)
+        return response
+    content_length = _parse_content_length(response.headers.get("content-length"))
+    if content_length is not None and content_length > cap:
+        raise ResponseTooLargeError(
+            status_code=response.status_code, limit=cap, content_length=content_length, reason="declared"
+        )
+    try:
+        content = _accumulate_capped(response.iter_bytes(), cap)
+    except _CapExceeded:
+        raise ResponseTooLargeError(
+            status_code=response.status_code, limit=cap, content_length=content_length, reason="streamed"
+        ) from None
+    return httpx2.Response(
+        status_code=response.status_code,
+        headers=_buffered_headers(response.headers),
+        content=content,
+        request=request,
+        extensions=_safe_extensions(response.extensions),
+        history=response.history,
+    )
+
+
+async def _read_capped_async(response: httpx2.Response, cap: int, request: httpx2.Request) -> httpx2.Response:
+    """Async mirror of `_read_capped` (counts decoded bytes from `aiter_bytes`)."""
+    if not _response_has_body(request.method, response.status_code):
+        await response.aread()  # empty body; preserve the original response (and its headers)
+        return response
+    content_length = _parse_content_length(response.headers.get("content-length"))
+    if content_length is not None and content_length > cap:
+        raise ResponseTooLargeError(
+            status_code=response.status_code, limit=cap, content_length=content_length, reason="declared"
+        )
+    buf = bytearray()
+    async for chunk in response.aiter_bytes():
+        buf += chunk
+        if len(buf) > cap:
+            raise ResponseTooLargeError(
+                status_code=response.status_code, limit=cap, content_length=content_length, reason="streamed"
+            )
+    return httpx2.Response(
+        status_code=response.status_code,
+        headers=_buffered_headers(response.headers),
+        content=bytes(buf),
+        request=request,
+        extensions=_safe_extensions(response.extensions),
+        history=response.history,
+    )

src/httpware/_internal/exception_mapping.py

@@ -1,11 +1,15 @@
-"""httpx2 -> httpware exception mapping.
+"""httpx2 -> httpware exception mapping + context-manager wrappers (shared).
 
-Pure function used by both Client._terminal and AsyncClient._terminal,
-and by both stream() methods. Clause ordering: TimeoutException ->
-InvalidURL/CookieConflict -> NetworkError -> HTTPError (subclass before
-parent so the right type wins).
+map_httpx2_exception is a pure function used by both Client._terminal and
+AsyncClient._terminal, and by both stream() methods. Clause ordering:
+TimeoutException -> InvalidURL/CookieConflict -> NetworkError -> HTTPError
+(subclass before parent so the right type wins). The two context managers
+below wrap it for use as `with`/`async with` blocks around the httpx2 call.
 """
 
+import contextlib
+from collections.abc import AsyncIterator, Iterator
+
 import httpx2
 
 from httpware.errors import NetworkError, TimeoutError, TransportError  # noqa: A004
@@ -26,3 +30,25 @@ def map_httpx2_exception(exc: BaseException) -> NetworkError | TimeoutError | Tr
     if isinstance(exc, httpx2.HTTPError):
         return TransportError(str(exc))
     return TransportError(str(exc))  # pragma: no cover — defensive default; httpx2.HTTPError is the root
+
+
+@contextlib.asynccontextmanager
+async def _httpx2_exception_mapper() -> AsyncIterator[None]:
+    """Map httpx2 exceptions to httpware exceptions. Shared by AsyncClient._terminal and stream()."""
+    try:
+        yield
+    except httpx2.HTTPError as exc:
+        raise map_httpx2_exception(exc) from exc
+    except (httpx2.InvalidURL, httpx2.CookieConflict) as exc:
+        raise map_httpx2_exception(exc) from exc
+
+
+@contextlib.contextmanager
+def _httpx2_exception_mapper_sync() -> Iterator[None]:
+    """Map httpx2 exceptions to httpware exceptions. Sync sibling of _httpx2_exception_mapper."""
+    try:
+        yield
+    except httpx2.HTTPError as exc:
+        raise map_httpx2_exception(exc) from exc
+    except (httpx2.InvalidURL, httpx2.CookieConflict) as exc:
+        raise map_httpx2_exception(exc) from exc