Bind document tools at call time and retain shared GitHub clients

Assistant-model: GPT-6 Sol
Assistant-workflow: harness-stack (run f6f676b9-6506-489b-93e2-2616ea55c6a8)
Assistant-duration: 61m blocked, estimated 60m
Assistant-verification: Bun focused unit passed: 48/48 document, hosted repository, and GitHub tool tests
Assistant-verification: Bun targeted regression passed: chat-started provenance 1/1 after fixture repair
Assistant-verification: Bun ci passed: mise exec -- bun run ci (dprint, oxlint, tokens)
Assistant-verification: Bun typecheck passed: mise exec -- bun run types (workspaces and E2E)
Assistant-verification: Bun unit passed: mise exec -- bun test (1555 pass, 2 PostgreSQL skips)
Assistant-verification: Playwright E2E passed: mise exec -- bun run e2e --workers=1 (230/230, fresh build)
Assistant-verification: agent-browser Edge manual scenario unavailable: GitHub Next SSO authorization left the chopin project Access unavailable; no @chopin file-and-PR citation observed
Assistant-verification: qlty metrics passed: document and GitHub tool sources analyzed
Co-authored-by: Alex Lavaee <lavaman131@github.com>