fix(pipeline): grade built-in deterministic assertions in subagent mode

[christso]

Summary

• pipeline input now writes built-in deterministic assertion configs (contains, regex, equals, etc.) to builtin_graders/ directory alongside existing code_graders/ and llm_graders/
• pipeline grade evaluates these built-in assertions in-process against response.md and writes results to code_grader_results/ so pipeline bench merges them into the final score
• pipeline bench reads the type field from result JSON instead of hardcoding 'code-grader', preserving the original assertion type in output

Red/Green Evidence

Red (main) — builtin assertions silently ignored:

Graded 0 code-grader(s): 0 passed
Benchmark: 1 test(s), pass_rate=0
score: 0, scores: []

Green (this branch) — builtin assertions evaluated correctly:

Graded 2 built-in assertion(s): 2/2 passed
Benchmark: 1 test(s), pass_rate=1
score: 1, scores: [{type: "contains", score: 1}, {type: "regex", score: 1}]

Test plan

• Unit tests: 5 new tests covering contains pass/fail, regex, negate, and input extraction
• Full test suite: 2133 tests pass, zero regressions
• Manual e2e: red/green verified with real pipeline run
• Pre-push hooks: build, typecheck, lint, test, validate all pass

Closes #1075

🤖 Generated with Claude Code

[cloudflare-workers-and-pages]

Deploying agentv with    Cloudflare Pages

Latest commit:	729b85c
Status:	✅  Deploy successful!
Preview URL:	https://a33d76a4.agentv.pages.dev
Branch Preview URL:	https://fix-1075-builtin-graders.agentv.pages.dev

View logs