feat(net): hyper leaf buffering (BufferMode::Buffer arm)

[NotAProfDev]

Closes #91. Second and final PR of the hyper-backend slice (PR A was #90).

Adds the `BufferMode::Buffer` branch to `HyperLeaf::call`: when a request carries a `BufferMode::Buffer` extension, the leaf collects the `Incoming` response body into `Bytes` inside the retry boundary (mapping the collect error with the same `map_hyper_err` as the streaming arm) and returns `ResponseBody::buffered`. The default (no extension) and explicit `BufferMode::Stream` keep the PR A streaming arm unchanged.

Additive only — no change to `type Response`/`type Error`/`HyperBody`/`ConnConfig`/`hyper_leaf`/`build()` or any resilience layer.

Commits:

• `feat(net): hyper leaf BufferMode::Buffer arm`
• `docs(net): changelog + module doc for hyper leaf buffering`
• `test(net): buffered error path surfaces from call()`

Tests: buffered request → `Buffered` arm carrying exact bytes; default + explicit `Stream` → `Streaming` arm; buffered mid-body failure surfaces as `Err(HttpError::Other)` from `call()` (proving retry coverage). `just ci` + `just msrv` green.

Design: docs/superpowers/specs/2026-07-05-net-http-hyper-backend-design.md
Plan: docs/superpowers/plans/2026-07-05-net-http-hyper-backend-pr-b.md

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • The net-http hyper backend now honors per-request BufferMode to control response buffering.
  • Requests that set BufferMode::Buffer receive an eagerly buffered response body; otherwise responses remain streamed.

• Bug Fixes

  • Truncated buffered responses now fail immediately during the request call (not later during body collection).
  • Added test coverage to verify buffered vs. streaming behavior, including explicit streaming mode.

[coderabbitai]

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• CHANGELOG.md

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📝 Walkthrough

Walkthrough

The hyper backend’s Service::call now reads BufferMode from request extensions to choose buffered or streaming response-body handling. Tests cover buffered, streaming, and truncated-body cases, and the changelog records the behavior.

Changes

BufferMode-driven Response Handling

Layer / File(s)	Summary
BufferMode branching in Service::call crates/adapter/net/http/hyper/src/leaf.rs	Service::call reads BufferMode from request extensions (defaulting to Stream) and returns either a buffered or streaming ResponseBody; updated imports and doc comments reflect the new behavior.
Tests for buffering and streaming behavior crates/adapter/net/http/hyper/src/leaf.rs	New tests verify Buffer yields ResponseBody::Buffered with correct bytes, absent/Stream yields ResponseBody::Streaming, and truncated bodies under Buffer fail during call() itself.
Changelog documentation CHANGELOG.md	Documents the new per-request BufferMode buffering behavior as additive with no API/type changes.

Estimated code review effort: 2 (Simple) | ~15 minutes

Possibly related PRs

• NotAProfDev/oath#60: Introduced the BufferMode/ResponseBody contract API that this PR's hyper leaf now consumes.

Suggested labels: enhancement

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title follows Conventional Commits and accurately summarizes the BufferMode::Buffer hyper leaf change.
Linked Issues check	✅ Passed	The changes implement #91: buffered handling for BufferMode::Buffer, while preserving default and Stream streaming behavior.
Out of Scope Changes check	✅ Passed	The doc and test updates support the requested hyper leaf buffering work and do not appear unrelated to #91.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/net-http-hyper-buffer

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@CHANGELOG.md`:
- Around line 114-118: Replace the unresolved PR placeholder in the changelog
entry with the actual pull request number or link. Update the `CHANGELOG.md`
entry for the net-http hyper backend note so the `(#<PR-B>)` reference uses the
real PR identifier, keeping the rest of the `ResponseBody::buffered` description
unchanged.

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• CHANGELOG.md
• crates/adapter/net/http/hyper/src/leaf.rs