docs: add PRD 0041

docs/prds/0041-git-http-request-bounds.md

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+# PRD 0041: Git HTTP Request Bounds
+
+- **Status:** Draft
+- **Author:** didericis-codex
+- **Created:** 2026-06-02
+- **Issue:** #138
+
+## Summary
+
+Add Content-Length validation and a body-size cap to `git_http_backend.py` so
+malformed or oversized smart-HTTP requests fail cleanly rather than crashing
+the handler or exhausting memory.
+
+## Problem
+
+`bot_bottle/git_http_backend.py` calls `int(self.headers.get("Content-Length",
+0))` without catching `ValueError`. A request with a non-numeric Content-Length
+raises an unhandled exception in the request handler.
+
+The handler reads the full declared length into memory before passing the body
+to `git http-backend` with no upper bound. A local or compromised client can
+force arbitrarily high memory use. For comparison, `supervise_server.py` caps
+request bodies at 1 MiB.
+
+## Goals / Success Criteria
+
+- A missing or non-numeric Content-Length returns HTTP 400.
+- A negative Content-Length returns HTTP 400.
+- A body larger than the cap (1 MiB, matching `supervise_server.py`) returns
+  HTTP 413.
+- Valid Git smart-HTTP pushes and fetches continue to work.
+- Unit tests cover: missing length, non-numeric length, negative length,
+  over-cap length, and a valid push/fetch passthrough.
+
+## Non-goals
+
+- No changes to git-gate authentication or route logic.
+- No changes to `supervise_server.py`.
+- No streaming / chunked-transfer-encoding support.
+- No TLS changes.
+
+## Scope
+
+In scope:
+
+- `bot_bottle/git_http_backend.py` request parsing and body reading.
+- Unit tests in `tests/unit/test_git_http_backend.py`.
+
+Out of scope:
+
+- Integration tests that drive a real Git client through the handler.
+
+## Design
+
+Wrap the Content-Length parse in a try/except and return 400 on `ValueError`.
+Add an explicit check for negative values. After parsing, compare the declared
+length against a module-level `_MAX_BODY_BYTES` constant (default 1 MiB) and
+return 413 if exceeded. Read exactly `min(content_length, _MAX_BODY_BYTES)`
+bytes.
+
+## Testing Strategy
+
+- Unit tests using `unittest.mock` to drive the handler with crafted headers.
+- Test cases: no Content-Length header, `Content-Length: abc`, `Content-Length:
+  -1`, `Content-Length: 2097152` (over cap), and a normal small POST body.
+
+Run:
+
+- `python3 -m unittest tests.unit.test_git_http_backend`
+- `python3 -m unittest discover -s tests/unit`
+
+## Open Questions
+
+None.