install ratcheting line-coverage gate at 34% floor (T-90)

First child of T-89. Codifies "don't make coverage worse" as a
durable pre-push contract before any test-writing children land.

- pubspec.yaml: new `coverage_floor: 34` key. Single source of
  truth for the floor; ratchets up only.
- ci/coverage_gate.sh: parses coverage/lcov.info (LH/LF), reads
  the floor from pubspec.yaml, exits non-zero if integer-truncated
  measured % drops below it. Self-contained awk parser — no `lcov`
  CLI dependency.
- ci/test.sh: flutter test now runs with --coverage, so the gate
  reads fresh data without an extra test invocation. Wall time
  delta is small and stays inside the < 90 s pre-push budget
  (D-29).
- Makefile: new `coverage-gate` target wires the script in;
  `push-check` adds it as a dependency. The .githooks/pre-push
  hook (already wired) picks this up automatically.
- .gitignore: ignore /coverage/ wholesale; the floor lives in
  pubspec.yaml, nothing under coverage/ is committed.

Decision recorded as D-66 (decisions/testing.md). End target is
95%; reaching it is tracked as the rest of T-89's children.

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

ci/coverage_gate.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+# Coverage gate — fails if total line coverage drops below the
+# `coverage_floor:` value in pubspec.yaml. Driven by D-66.
+#
+# Reads coverage/lcov.info (generated by `flutter test --coverage`,
+# which `ci/test.sh` runs as part of the fast suite). Parses the
+# total LF/LH counts and compares the integer percentage against
+# the floor. The floor only ratchets up — bumping it requires an
+# explicit edit to pubspec.yaml committed alongside the test
+# additions that earned the bump.
+#
+# Self-contained parser (awk) — does not depend on `lcov` being
+# installed on the dev machine.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+LCOV=coverage/lcov.info
+
+if [[ ! -f "$LCOV" ]]; then
+  echo "==> coverage gate: $LCOV missing — run \`make test\` first (it writes lcov)" >&2
+  exit 2
+fi
+
+floor=$(awk -F: '/^coverage_floor:/ {gsub(/ /,"",$2); print $2; exit}' pubspec.yaml)
+if [[ -z "$floor" ]]; then
+  echo "==> coverage gate: pubspec.yaml is missing coverage_floor: — see D-66" >&2
+  exit 2
+fi
+read measured measured_int < <(
+  awk -F: '
+    /^LF:/ { lf += $2 }
+    /^LH:/ { lh += $2 }
+    END {
+      pct = (lh / lf) * 100
+      printf "%.2f %d\n", pct, int(pct)
+    }
+  ' "$LCOV"
+)
+
+if (( measured_int < floor )); then
+  echo "==> coverage gate FAIL: ${measured}% < floor ${floor}%"
+  echo "    Add tests, or — if the drop is intentional — explain in the commit and lower the floor explicitly."
+  exit 1
+fi
+
+if (( measured_int > floor )); then
+  echo "==> coverage gate OK: ${measured}% (floor ${floor}%) — ${measured_int}% available; consider bumping coverage/floor.txt to ${measured_int}"
+else
+  echo "==> coverage gate OK: ${measured}% (floor ${floor}%)"
+fi

ci/test.sh

@@ -14,5 +14,5 @@ dart format --set-exit-if-changed .
 echo "==> dart test (forkpty — incompatible with flutter test runner)"
 dart test --tags forkpty test/pty/session_test.dart
 
-echo "==> flutter test (unit + widget + golden)"
-flutter test --exclude-tags forkpty
+echo "==> flutter test --coverage (unit + widget + golden)"
+flutter test --coverage --exclude-tags forkpty