feat(core): add copilot-cli provider

[christso]

Summary

• Adds copilot-cli built-in provider kind that invokes GitHub Copilot CLI via -s --allow-all-tools --no-color -p <prompt>
• Follows same patterns as codex/claude-code providers (workspace, preread, stream logging)
• Includes target validation, CLI log subscription, example config, and unit tests

Closes #127

Test plan

• 9 unit tests for provider invocation, ANSI stripping, timeout, error handling, model args, custom args, input files, log streaming
• bun run build && bun run typecheck && bun run lint && bun test all pass (385 tests, 0 failures)
• E2E: 3 concurrent eval cases with gpt-4.1 (math, code gen, multi-line) — all pass
• E2E: gpt-5-mini model — passes
• E2E: custom system_prompt override — passes
• E2E: timeout handling (1s timeout correctly reports "timed out after 1s")
• E2E: concurrent workers (3 default) confirmed working
• E2E: log files created in .agentv/logs/copilot-cli/ with proper headers and timestamps

🤖 Generated with Claude Code

[christso]

Cancelling this openspec proposal.

Reason: GitHub Copilot CLI lacks structured JSON output (no --json or --output-format flag), unlike Codex, Pi, and Claude Code providers which all support JSONL event streams with tool call traces.

This means copilot-cli targets would:

• Not support tool trajectory evaluators
• Have no structured trace data
• Be limited to final text output only

The existing agent providers (Codex, Pi, Claude Code) are sufficient for our needs and all provide full observability.

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[christso]

Code Review: PR #127 — Add copilot-cli Provider

Verification Results

Check	Result
bun run build	PASS
bun run typecheck	PASS
bun run lint	PASS (212 files, no issues)
bun run test	PASS (385 tests across 28 files)

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What Was Done Well

• Pattern consistency — closely mirrors the codex provider structure, making the codebase predictable and maintainable
• Testability — constructor accepts a CopilotCliRunner function for dependency injection, enabling clean unit tests without spawning real processes
• Test coverage — 9 unit tests covering happy path, ANSI stripping, non-zero exit, timeout, empty output, model flag, custom args, input files/preread, and log streaming
• Clean integration — CLI log subscription and progress display follow the exact same pattern as codex/pi providers
• Alias removal — final commit removing copilot/github-copilot aliases is a justified deviation from the proposal, keeping a single canonical copilot-cli name

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Issues — Should Fix

1. Security: Unescaped shell argument in locateExecutable (copilot-cli.ts:454)

const { stdout } = await execAsync(`${locator} ${candidate}`);

The candidate string from user YAML config is interpolated into a shell command without escaping. This is a pre-existing pattern from the codex provider, but propagating it further isn't ideal. Recommendation: use execFile instead of exec, or sanitize/quote the candidate. Could be addressed as a follow-up across all providers.

2. Prompt passed as CLI argument may hit OS ARG_MAX limits (copilot-cli.ts:90,170)

The full prompt (system prompt + base prompt with file contents) is passed via -p as a command-line argument. Linux ARG_MAX is typically ~2MB. Large evaluations could fail with E2BIG. The codex provider avoids this by piping via stdin (child.stdin.end(options.prompt)), while copilot-cli closes stdin immediately. Recommendation: investigate if Copilot CLI supports --prompt-file or stdin input; otherwise add a size check with a clear error.

3. Missing AGENTV_COPILOT_LOG_FORMAT env var fallback (targets.ts:950-952)

The codex resolver falls back to env.AGENTV_CODEX_LOG_FORMAT, but the copilot resolver has no equivalent env var fallback. Users setting log format via environment variables (common in CI) would expect parity. Recommendation: add env.AGENTV_COPILOT_LOG_FORMAT as a fallback in resolveCopilotConfig.

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Suggestions — Nice to Have

4. Significant code duplication with codex provider — CopilotCliStreamLogger and several utility functions (buildLogFilename, sanitizeForFilename, formatElapsed, pickDetail, etc.) are duplicated near-verbatim. Consider extracting shared utilities if more CLI providers are planned.

5. ANSI stripping covers CSI and OSC sequences, which is sufficient for --no-color output, but doesn't cover 8-bit CSI (\x9B). Minor concern.

6. hasPrintedLogHeader flag in progress-display.ts — first provider to emit logs claims the header label; copilot logs appearing after codex logs won't get their own header. Pre-existing issue.

7. Tests should verify -p is the last argument pair — the code comments say this is required (copilot-cli.ts:169) but tests don't assert argument ordering. An assertion like expect(invocation.args.indexOf('-p')).toBe(invocation.args.length - 2) would catch regressions.

8. Pre-existing: system_prompt/systemPrompt missing from CODEX_SETTINGS validator — the copilot provider correctly includes these, but the codex validator set is missing them (causes spurious warnings). Not introduced by this PR.

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Final Assessment

This is a well-executed PR that follows established codebase patterns. Issues #1-#3 should be discussed before merge, with #2 (argument length limits) being the most impactful for real-world usage. The remaining suggestions can be addressed as follow-ups.

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