chore(coverage): relax thresholds to cut low-value churn

Lower the diff-coverage gate from 90% to 80% and the critical-module
target from 90% to 85%. The 90% diff gate forced back-fill tests on
nearly every changed line; 80% keeps new code honest without the churn.
Global coverage stays informational per ADR 0004 (no new gate added).

Updates scripts/diff_coverage.py, scripts/coverage.sh,
scripts/critical-modules.txt, .gitea/workflows/test.yml, and records the
change as a dated revision in ADR 0004.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/test.yml

@@ -298,7 +298,7 @@ jobs:
       - name: Combined coverage (unit + docker integration)
         run: PYTHON=python3 bash scripts/coverage.sh aggregate critical
 
-      - name: Diff-coverage gate (changed lines >= 90%)
+      - name: Diff-coverage gate (changed lines >= 80%)
         run: |
           git fetch --no-tags origin main:refs/remotes/origin/main
-          python3 scripts/diff_coverage.py --base origin/main --min 90
+          python3 scripts/diff_coverage.py --base origin/main --min 80

docs/decisions/0004-coverage-policy.md

@@ -3,6 +3,10 @@
 - **Status:** Accepted
 - **Date:** 2026-06-25
 - **Deciders:** didericis
+- **Revised:** 2026-07-27 — thresholds relaxed (critical minimum 90→85%,
+  diff-coverage gate 90→80%) to cut low-value test churn on changed lines.
+  The risk-weighting structure and the "global is informational" rule are
+  unchanged.
 
 ## Context
 
@@ -34,7 +38,7 @@ a regression (Goodhart's law).
 Coverage is **risk-weighted**, measured over the **combined unit +
 integration** suites, with three rules:
 
-1. **Critical modules must remain ≥ 90%.** The curated security/logic core
+1. **Critical modules must remain ≥ 85%.** The curated security/logic core
    covers the host and gateway egress policy, manifest trust boundary,
    git-gate enforcement, supervise protocol/server, YAML parser, and bottle
    state. The concrete module list lives in `scripts/critical-modules.txt`;
@@ -55,7 +59,7 @@ integration** suites, with three rules:
 
 The forward-looking guard is a **diff-coverage gate**
 (`scripts/diff_coverage.py`): new/changed executable lines on a branch
-must be ≥ 90% covered. This catches regressions where they are
+must be ≥ 80% covered. This catches regressions where they are
 introduced without forcing a back-fill crusade through legacy glue. The
 gate skips lines in omitted files (there is no coverage data for them),
 so the omit list cannot launder *new* logic into the dark: anything that

scripts/coverage.sh

@@ -13,7 +13,7 @@
 #     are re-executed; no KVM or Docker dependency.
 #
 # Pass "critical" as the last argument in either mode to also report just the
-# critical modules (ADR 0004 target: 90%).
+# critical modules (ADR 0004 target: 85%).
 set -euo pipefail
 
 cd "$(dirname "$0")/.."
@@ -34,8 +34,8 @@ if [ "${1:-}" = "aggregate" ]; then
     "$PY" -m coverage report -m
 
     if [ "${2:-}" = "critical" ]; then
-        echo "== critical modules (ADR 0004 minimum: 90%) ==" >&2
-        "$PY" -m coverage report --include="$CRITICAL" --fail-under=90
+        echo "== critical modules (ADR 0004 minimum: 85%) ==" >&2
+        "$PY" -m coverage report --include="$CRITICAL" --fail-under=85
     fi
     exit 0
 fi
@@ -55,6 +55,6 @@ echo "== combined report ==" >&2
 "$PY" -m coverage report -m
 
 if [ "${1:-}" = "critical" ]; then
-    echo "== critical modules (ADR 0004 minimum: 90%) ==" >&2
-    "$PY" -m coverage report --include="$CRITICAL" --fail-under=90
+    echo "== critical modules (ADR 0004 minimum: 85%) ==" >&2
+    "$PY" -m coverage report --include="$CRITICAL" --fail-under=85
 fi

scripts/critical-modules.txt

@@ -1,4 +1,4 @@
-# Critical security/logic core held to the >=90% coverage bar by
+# Critical security/logic core held to the >=85% coverage bar by
 # docs/decisions/0004-coverage-policy.md.
 #
 # SINGLE SOURCE OF TRUTH: scripts/coverage.sh (the `critical` report) and

scripts/diff_coverage.py

@@ -13,8 +13,8 @@ policy.
 
 Usage:
     scripts/coverage.sh                 # produce .coverage first
-    python3 scripts/diff_coverage.py    # gate against origin/main, min 90%
-    python3 scripts/diff_coverage.py --base main --min 85
+    python3 scripts/diff_coverage.py    # gate against origin/main, min 80%
+    python3 scripts/diff_coverage.py --base main --min 75
 """
 
 from __future__ import annotations
@@ -74,7 +74,7 @@ def main() -> int:
     ap = argparse.ArgumentParser()
     ap.add_argument("--base", default="origin/main",
                     help="git ref to diff against (default: origin/main)")
-    ap.add_argument("--min", type=float, default=90.0,
+    ap.add_argument("--min", type=float, default=80.0,
                     help="minimum %% of changed executable lines covered")
     args = ap.parse_args()