## Problem
External audit flagged critical security-path files at 0% coverage:
- workspace-server/handlers/tokens.go 0% (target 90%+)
- workspace-server/handlers/workspace_provision 0% (target 75%+)
- workspace-server/middleware/wsauth ~48% (target 90%+)
Tests *exist* for these files (tokens_test.go is 200 lines, workspace_
provision_test.go is 1138 lines) — they just don't exercise the critical
branches where auth/provisioning decisions happen. CI's existing coverage
step measured total coverage (floor 25%) but never checked per-file,
so any single file could drop to 0% and CI stayed green.
## Fix — Layer 1 of #1823 (strictly additive)
1. **Per-file coverage report** — advisory step prints every source file
with its coverage, sorted worst-first. Reviewers see the gap at a
glance. Does not fail the build.
2. **Critical-path per-file gate** — if any non-test source file in a
security-sensitive directory (tokens, workspace_provision, a2a_proxy,
registry, secrets, wsauth, crypto) has coverage ≤10%, CI fails with
a specific error message pointing at the file + #1823.
3. **Unchanged: total floor stays at 25%** — ratcheting is a separate PR
so this one has zero risk of breaking existing coverage. Ratchet plan
lives in COVERAGE_FLOOR.md (monthly schedule through Oct 2026 to reach
70% total / 70% critical).
## Why this specifically
"Tell devs to write tests" doesn't fix this — the prompts already
require tests ("Write tests for every handler, every query, every edge
case"), and the engineers mostly do. The gap is mechanical: CI generates
coverage.out and throws it away without checking per-file distribution.
This gate makes "no untested security path merges" a property of the CI,
not a property of QA agents who (as of today's incident) can go phantom-
busy for hours.
## Smoke test
Local awk-logic verification with synthetic coverage.out:
- tokens.go at 2.5% (critical path, ≤10%) → correctly FAILS
- noncritical.go at 0.0% (not in critical list) → correctly PASSES
- wsauth_middleware.go at 65% (critical, above 10%) → correctly PASSES
- crypto/kek.go at 85% (critical, above 10%) → correctly PASSES
Regex bug caught and fixed: go tool cover -func emits
file.go:LINE.COL:FUNC PERCENT
The stripper needed :[0-9]+\..* not :[0-9]+:.*
## Follow-up (not in this PR)
- Layer 2 (issue #1823): per-changed-file delta gate via diff-cover,
enforcing the prompt rule ">80% on changed files"
- Add these two new steps to branch protection required checks
- Canvas (Next.js) equivalent with vitest --coverage + threshold
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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