Improve Agent Host E2E test coverage

[roblourens]

Summary

• add host-only E2E coverage for AHP lifecycle, subscriptions, active-client creation, filesystem defaults, and Git-backed changesets
• verify exact multiline Markdown response preservation across Claude, Codex, and Copilot
• make host-only known-issue reproductions runnable in strict replay without credentials
• document the duplicate-session creation contract gap

Coverage

Compared with the original fresh baseline:

• lines/statements: 75.77% to 75.89% (+131 covered, +0.12pp)
• branches: 66.31% to 66.59% (+77 covered, +0.28pp)
• functions: 70.97% to 71.19% (+9 covered, +0.22pp)

Native V8 branch denominators vary slightly between otherwise identical runs.

Validation

• npm run test-agent-host-e2e-coverage
• focused replay for all new host-only declarations
• replay for the multiline Markdown test across Claude, Codex, and Copilot
• host-only recording check confirming no fixture is created
• npm run typecheck-client
• npm run valid-layers-check
• hygiene checks and git diff --check

(Written by Copilot)

[Copilot]

Pull request overview

Expands Agent Host E2E coverage for protocol lifecycle, filesystem defaults, changesets, and provider response fidelity.

Changes:

• Adds host-only protocol, subscription, filesystem, and Git changeset scenarios.
• Verifies exact multiline Markdown preservation across three providers.
• Enables strict-replay known-issue coverage and updates coverage data.

Show a summary per file

File	Description
protocolContractsSuite.ts	Adds lifecycle, session, active-client, and subscription tests.
e2eTestContext.ts	Adds host-only known-issue control.
coreSuite.ts	Tests multiline Markdown preservation.
clientFilesystemSuite.ts	Covers default filesystem behavior.
changesetSuite.ts	Expands Git changeset scenarios.
agentHostE2ESuites.ts	Wires host-only known-issue execution.
KNOWN_ISSUES.md	Documents duplicate-session behavior.
coverage/summary.json	Refreshes coverage results.
copilotcli-…markdown-response.yaml	Adds Copilot CLI replay capture.
codex-…markdown-response.yaml	Adds Codex replay capture.
claude-…markdown-response.yaml	Adds Claude replay capture.

Review details

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• Files reviewed: 10/11 changed files
• Comments generated: 0
• Review effort level: Balanced