diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 4f204a7..810f8c5 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -3,3 +3,12 @@
 All instructions for this repository are maintained in [`AGENTS.md`](../AGENTS.md) at the repository root.
 
 Please read and follow the guidance in that file.
+
+## Tech Stack
+
+- **Runtime:** Google Apps Script (V8) for deployed code; Node.js for tooling and tests
+- **Language:** JavaScript (`.gs` / `.js`), with TypeScript available for type checking (`npm run typecheck`)
+- **Testing:** Jest (unit, `npm test`) · Playwright (e2e, `npm run test:e2e`)
+- **Linting:** ESLint + Prettier (`npm run check`)
+- **Coverage thresholds:** 99% lines, 95% statements/functions, 85% branches
+- **Key libraries:** `@types/google-apps-script` (GAS type defs), `ts-jest`, `husky` + `lint-staged` (pre-commit), `@commitlint` (conventional commits)
diff --git a/AGENTS.md b/AGENTS.md
index 3af9de4..fb12866 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -33,7 +33,7 @@ This file follows the AGENTS.md conventions (see https://agents.md/) and provide
 
 ## Tests & CI (repo conventions)
 
-- **Coverage thresholds:** 100% lines, 95% statements/functions, 85% branches. Verify locally with `npm test -- --coverage` (or `npx jest --coverage`) and ensure CI coverage meets these requirements. PRs that reduce coverage below these thresholds will be rejected.
+- **Coverage thresholds:** 99% lines, 95% statements/functions, 85% branches. Verify locally with `npm test -- --coverage` (or `npx jest --coverage`) and ensure CI coverage meets these requirements. PRs that reduce coverage below these thresholds will be rejected.
 - Before requesting review or marking a PR as ready:
   - Run `npm test` and ensure all tests pass locally
   - Run `npm test -- --coverage` and ensure coverage meets thresholds
diff --git a/CLAUDE.md b/CLAUDE.md
index 69cb05d..5d97a9f 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -17,7 +17,7 @@ This file provides Claude Code-specific instructions. For comprehensive agent gu
 ## Key Rules
 
 1. **TDD is mandatory** — write tests before implementation, include tests in the same PR
-2. **Coverage thresholds** — 100% lines, 95% statements/functions, 85% branches
+2. **Coverage thresholds** — 99% lines, 95% statements/functions, 85% branches
 3. **Avoid coverage-ignore comments and `.skip()`** — only use in rare, unavoidable cases (per AGENTS.md) with clear justification
 4. **GAS testing pattern** — extract logic to `src/index.js` with `module.exports`, inject GAS services as parameters
 5. **Always run** `npx prettier --write .` before committing — pre-commit hooks don't run in agent sessions