feat(bot): natural-language pre-merge checks (Phase 5)

[lohitkolluri]

What

Adds configurable natural-language pre-merge checks: per-repo [[pre_merge.checks]] entries (name, mode off|warning|error, optional scope glob, instructions) evaluated by the BYOK LLM against the PR diff.

How

• src/bot/premerge.rs: run_pre_merge_checks — scope-filtered, offline fail-closed (inconclusive never blocks), persists each run to pre_merge_check_runs
• src/llm/mod.rs: premerge_check — strict two-line output contract (PASSED/FAILED/INCONCLUSIVE + reasoning), diff truncated to 20k chars, untrusted-content delimiters
• src/config.rs: PreMergeCheck + checks on PreMergeConfig
• src/db/migrations.rs: v20 pre_merge_check_runs table (PK repo+pr+check)
• src/bot/review/pipeline.rs: run before readiness; error-mode failures become readiness hard blockers (score 0) and fail the Codasaurus check run; results posted as PR comment + appended to check-run summary

Tests

245 lib tests pass (3 new: glob matching, scope filtering, offline inconclusive). fmt + clippy -D warnings clean.

Docs: docs/codasaurus-toml.md example for [[pre_merge.checks]].

[codasaurus-e0a6]

Codasaurus

This PR updates 7 files across src, docs. Automated checks look clear.

Changes

Path	What changed
docs/codasaurus-toml.md	updated
src/bot/mod.rs	updated
src/bot/premerge.rs	added
src/bot/review/pipeline.rs	updated
src/config.rs	updated
src/db/migrations.rs	updated
src/llm/mod.rs	updated

All files (7)

• docs/codasaurus-toml.md (modified)
• src/bot/mod.rs (modified)
• src/bot/premerge.rs (added)
• src/bot/review/pipeline.rs (modified)
• src/config.rs (modified)
• src/db/migrations.rs (modified)
• src/llm/mod.rs (modified)

[codasaurus-e0a6]

Context

Blast radius

Sensitive path: src/bot/mod.rs (+1)

Blast details

High-sensitivity paths:

• src/bot/mod.rs
• src/llm/mod.rs

_{Bounded estimate from PR imports only.}

Related pull requests

• Feat/symbol graph #25: Feat/symbol graph (3 shared files)
• feat: confidence score (0-5) + optional LLM judge #24: feat: confidence score (0-5) + optional LLM judge (3 shared files)
• feat: baseline finding suppression + quality gates #23: feat: baseline finding suppression + quality gates (2 shared files)

[codasaurus-e0a6]

Checks

All clear. Automated checks did not find anything to fix before merge.

Commands

Type as plain text (GitHub Apps are not @-mentionable):

review · describe · summarize · improve · security · ask … · ignore <fp> · help

_{Full list: @codasaurus help}