test: HTTP bounds for POST /p2p-draft-backup (closes #2198)

[RealDiligent]

Summary

• Closes [Bug]: POST /p2p-draft-backup persists host_peer_id/snapshot_json unbounded (WS path bounds them) #2198. guard_p2p_backup already bounds host_peer_id to MAX_TOKEN_LEN and snapshot_json to MAX_P2P_SNAPSHOT_LEN before SQLite persistence; this PR adds production-path HTTP integration tests so the endpoint contract cannot regress.
• Tests cover oversized host_peer_id, oversized snapshot_json, and a valid store returning 200 OK.

Test plan

• p2p_backup_post_rejects_oversized_host_peer_id
• p2p_backup_post_rejects_oversized_snapshot
• p2p_backup_post_accepts_valid_payload
• CI Rust tests (phase-server integration module)

Tier

Standard

Track

Non-developer

LLM

Model: claude-sonnet-4-6
Thinking: high

Gate A

No parser/oracle-text files changed. ./scripts/check-parser-combinators.sh has no parser surface to audit (CI will confirm exit 0).

Anchored on

• crates/server-core/src/p2p_backup_guard.rs:43 — guard_p2p_backup applies validate_token + snapshot byte cap at the HTTP boundary.
• crates/phase-server/src/admin.rs:111 — p2p_backup_store rejects invalid bodies with 400 before save_p2p_backup.
• crates/lobby-broker/src/validation.rs — MAX_TOKEN_LEN is the shared bound the WebSocket lobby path already enforces.

Verification

Local verification skipped — see CI status checks.

Scope Expansion

None.

Validation Failures

None.

CI Failures

None.

[gemini-code-assist]

Code Review

This pull request introduces a new test module p2p_backup_http_tests in crates/phase-server/src/main.rs to validate the P2P backup HTTP endpoints under various scenarios, such as oversized payloads and valid requests. The review feedback recommends replacing the single read call on the TCP stream with read_to_end to avoid partial reads and ensure robust, non-flaky test execution in CI environments.

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[gemini-code-assist]

[MEDIUM] Use read_to_end instead of a single read call to avoid partial reads of the HTTP response.

Why it matters: A single read call on a TCP stream is not guaranteed to read the entire response, which can lead to flaky test failures in CI environments under load. Since the request specifies Connection: close, we can safely read until EOF using read_to_end.

Suggested change

	let mut buf = vec![0u8; 64 * 1024];
	let n = stream.read(&mut buf).await.expect("read");
	let response = std::str::from_utf8(&buf[..n]).expect("utf8");
	let mut buf = Vec::new();
	stream.read_to_end(&mut buf).await.expect("read");
	let response = std::str::from_utf8(&buf).expect("utf8");

[matthewevans]

Thanks for putting together the HTTP boundary coverage. I am going to close this from the maintainer side rather than keep it in the queue.

For this endpoint, we are not taking a contributor test-only PR right now; the production validation path and any follow-up regression coverage will be handled in a maintainer-owned change. This head also is not queue-ready as-is: cargo fmt --check is failing in the Rust lint job, and the raw TCP test helper should read the full response rather than relying on a single read call.