Harden bounded real-client capture and preserve the accepted 0.1.7 profile #244

Context

Follow-up from the exact-SHA 0.1.7 qualification and PR #243. The accepted 0.1.7 candidate and its mixed automatic/manual profile remain immutable and reproducible.

0.1.8 uses the real Codex CLI as its only product-level acceptance seam. This issue hardens the shared capture/process infrastructure used by both profiles; the new declarative 0.1.8 profile itself belongs to #255.

Scope

• Preserve the accepted 0.1.7 profile, ordering, run binding, and artifacts as a versioned legacy profile.
• Make process output capture incrementally bounded instead of calling ReadToEndAsync before truncation.
• Use independent stdout/stderr rings with an explicit truncation/overflow result.
• Parse JSONL incrementally when it is case evidence; do not retain the complete raw stream.
• Ensure every transient root and child process is cleaned up on success, failure, timeout, cancellation, and harness interruption.
• Make failure timing assertions phase-local so cold Windows startup cannot masquerade as a slow failure classifier.
• Extend the evidence schema so cleanup and truncation outcomes are machine-readable.

0.1.8 boundary

• No Desktop, ZCode, or other GUI/manual interaction is part of 0.1.8 qualification.
• 0.1.8 Beta7: Add the versioned CLI-only release-verification profile #255 declares and executes the versioned 0.1.8 CLI-only cases.
• The shared runner may support both profiles, but changing 0.1.8 must not silently rewrite the accepted 0.1.7 matrix.
• The 0.1.8 evidence budgets are enforced by 0.1.8 RC1: Aggregate six fixed regression batches and publish promotion evidence #257: 64 KiB incremental rings per stdout/stderr stream, <=256 KiB successful case, <=4 MiB failed case, and <=16 MiB durable run upload.

Acceptance criteria

• The accepted 0.1.7 profile can still be selected and produces the same case contract without changing its historical qualified artifact.
• The 0.1.8 CLI-only profile can reuse the shared process/capture seam without opening GUI clients or requesting manual evidence.
• Output exactly below, at, and above each configured bound is covered by deterministic fixtures.
• Overflow/truncation is explicit and fails closed whenever the omitted stream is required case evidence.
• JSONL parsing and stdout/stderr draining remain bounded under long output and backpressure.
• Success, ordinary failure, timeout, cancellation, and abrupt child/Gateway exit all prove process teardown and transient-root deletion.
• Phase-local timeout tests are independent of preflight and cold client startup.
• docs/agents/real-client-e2e.md documents profile selection, bounds, cleanup, and unattended watchdog use.

Scope guard

Test infrastructure only. Do not alter provider routing, runtime translation, release-channel behavior, or the accepted 0.1.7 artifact in this issue.