refactor(review): consolidate repo context into single sandbox tool

[ephor]

Remove read_repo_file, list_repo_dir, search_repo tools and the per-pass call budget system. All repository exploration now flows through run_repo_command against a persistent sandbox checkout.

Also rewrite the instruction to guide evidence-based investigation: concrete questions → targeted searches → callers/tests → iterate.

Changes

• repo-tools.ts: removed read_repo_file, list_repo_dir, search_repo, resolveToolBudget, isSafeRepoPath, guardedExecute; repoContextTools now returns only run_repo_command (+ dependency_review)
• instruction.ts: new ## Repository investigation section with numbered workflow steps
• review-pr.ts: removed fileCount parameter from repoContextTools calls
• env.ts: removed REPO_TOOL_CALL_BUDGET / REPO_TOOL_CALL_BUDGET_MAX env vars
• README.md: updated architecture and tool descriptions
• Tests: simplified, added test D for instruction content

Motivation

After switching to persistent sandbox checkout, the GitHub API file/list/search tools caused reviewers to clone once then abandon the checkout for slower, fragmented API reads. Single tool + good instructions > four tools with budget system.

[mimir-code-assist]

Mimir review — 🟢 No blocking issues

Clean refactor that consolidates all repository exploration behind the persistent sandbox checkout, removing three GitHub API-based tools (read_repo_file, list_repo_dir, search_repo) along with their budget system (REPO_TOOL_CALL_BUDGET, REPO_TOOL_CALL_BUDGET_MAX). The call-budget existed solely to rate-limit GitHub API calls — with those tools removed, it has no purpose. All call sites, env-schema definitions, documentation, and tests are updated consistently. The sandbox command remains bounded by timeout (60s) and output size (20K chars), and path-traversal protection is already covered by isSafeSandboxCommand. The replacement instruction guidance is more thorough and principled.

Findings: 0 critical · 0 major · 0 minor · 0 nit

_{💰 Review cost: $0.0166 — primary deepseek/deepseek-v4-flash $0.0166}