test: add unit tests for 6 previously-untested packages (R7)

Added pure unit tests for all packages that had 0% coverage. Where pure
logic was entangled with DB calls, extracted testable helpers first.

internal/domain (0% -> 100%):
- TestIsNil, TestCanTransition (all 30 state transitions), TestSentinelErrors,
  TestSignalTransitionsComplete

internal/learning (0% -> 26.2%):
- Refactored processGroup to extract 4 pure helpers: countOutcomes,
  computeConfidence, shouldValidate, shouldQuarantine
- TestWilsonLowerBound (monotonicity, edge cases, sample-size cap)
- TestCountOutcomes, TestComputeConfidence, TestShouldValidate,
  TestShouldQuarantine (table-driven)
- Remaining gap: extractPatterns/processGroup DB calls need make test-db

internal/policy (39% -> 50%):
- Extracted determineRoute from ClassifySignal (pure route logic)
- TestDetermineRoute (7 cases covering global/entity kill-switches, approval)
- Remaining gap: ClassifySignal/computeBlastRadius need DB mock

internal/knowledge (0% -> 14.2%):
- TestContentHash, TestStr, TestStrSlice, TestMapVal, TestToPGArray
- Documented latent bug: toPGArray doesn't escape " or \\ in tags
- Remaining gap: ingest* functions need make test-db

internal/actuator (0% -> 14.7%):
- TestSSHErrorClassString, TestClassifySSHError (11 cases incl. net.Error mock)
- TestParseProcedure, TestSetDefaultSSHTimeout
- Circuit breaker full state-machine test (open/close/reset/per-target)
- Remaining gap: ExecuteProcedure/ProvisionLXC need SSH+DB fixtures

internal/scheduler (0% -> 7.3%):
- TestParsePingLatency (Linux/macOS formats), TestAllowlistedScript
- TestEvaluateSeverity (threshold logic, crit:0 skip, signalKind fallback)
- Remaining gap: checkHTTP/checkTCP need httptest; runCheckPass needs DB

internal/notifier (0% -> 6.4%):
- TestHashToken, TestGenerateApprovalToken (HMAC re-derivation)
- Remaining gap: checkReaction/sendMatrixAlert need httptest; DB funcs need
  make test-db

All tests pass with -race. domain hits its 60% gate at 100%. The remaining
packages need integration tests (make test-db) and/or httptest-based tests
to reach their coverage gates — tracked as follow-up.

internal/knowledge/seed_test.go

@@ -0,0 +1,155 @@
+package knowledge
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"reflect"
+	"testing"
+)
+
+func TestContentHash(t *testing.T) {
+	t.Run("determinism", func(t *testing.T) {
+		a := contentHash("hello")
+		b := contentHash("hello")
+		if a != b {
+			t.Errorf("contentHash not deterministic: %q != %q", a, b)
+		}
+	})
+
+	t.Run("empty string known sha256", func(t *testing.T) {
+		got := contentHash("")
+		h := sha256.Sum256([]byte(""))
+		want := hex.EncodeToString(h[:])
+		if got != want {
+			t.Errorf("contentHash(\"\") = %q, want %q", got, want)
+		}
+	})
+
+	t.Run("different inputs different outputs", func(t *testing.T) {
+		if contentHash("a") == contentHash("b") {
+			t.Error("different inputs produced same hash")
+		}
+	})
+
+	t.Run("output is 64-char hex", func(t *testing.T) {
+		got := contentHash("anything")
+		if len(got) != 64 {
+			t.Errorf("len = %d, want 64", len(got))
+		}
+		for _, r := range got {
+			isHex := (r >= '0' && r <= '9') || (r >= 'a' && r <= 'f')
+			if !isHex {
+				t.Errorf("non-hex char %q in hash %q", r, got)
+				break
+			}
+		}
+	})
+}
+
+func TestStr(t *testing.T) {
+	cases := []struct {
+		name string
+		m    map[string]any
+		key  string
+		want string
+	}{
+		{"missing key", map[string]any{}, "nope", ""},
+		{"string value", map[string]any{"k": "v"}, "k", "v"},
+		{"int value", map[string]any{"k": 42}, "k", ""},
+		{"nil value", map[string]any{"k": nil}, "k", ""},
+		{"empty string", map[string]any{"k": ""}, "k", ""},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := str(c.m, c.key)
+			if got != c.want {
+				t.Errorf("str() = %q, want %q", got, c.want)
+			}
+		})
+	}
+}
+
+func TestStrSlice(t *testing.T) {
+	cases := []struct {
+		name string
+		m    map[string]any
+		key  string
+		want []string
+	}{
+		{"missing key", map[string]any{}, "tags", nil},
+		{"all strings", map[string]any{"tags": []any{"a", "b", "c"}}, "tags", []string{"a", "b", "c"}},
+		{"mixed types", map[string]any{"tags": []any{1, "a", true, "b"}}, "tags", []string{"a", "b"}},
+		{"empty array", map[string]any{"tags": []any{}}, "tags", []string{}},
+		{"nil elements filtered", map[string]any{"tags": []any{nil, "a", nil, "b"}}, "tags", []string{"a", "b"}},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := strSlice(c.m, c.key)
+			if len(got) != len(c.want) {
+				t.Errorf("len = %d, want %d (got %v)", len(got), len(c.want), got)
+				return
+			}
+			for i := range got {
+				if got[i] != c.want[i] {
+					t.Errorf("[%d] = %q, want %q", i, got[i], c.want[i])
+				}
+			}
+		})
+	}
+}
+
+func TestMapVal(t *testing.T) {
+	cases := []struct {
+		name string
+		m    map[string]any
+		key  string
+		want map[string]any
+	}{
+		{"missing key", map[string]any{}, "nope", nil},
+		{"present map", map[string]any{"k": map[string]any{"x": 1}}, "k", map[string]any{"x": 1}},
+		{"wrong type string", map[string]any{"k": "v"}, "k", nil},
+		{"nested map", map[string]any{"k": map[string]any{"a": map[string]any{"b": 2}}}, "k", map[string]any{"a": map[string]any{"b": 2}}},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := mapVal(c.m, c.key)
+			if !reflect.DeepEqual(got, c.want) {
+				t.Errorf("mapVal() = %v, want %v", got, c.want)
+			}
+		})
+	}
+}
+
+func TestToPGArray(t *testing.T) {
+	cases := []struct {
+		name string
+		tags []string
+		want string
+	}{
+		{"empty", []string{}, "{}"},
+		{"single", []string{"a"}, `{"a"}`},
+		{"multiple", []string{"a", "b"}, `{"a","b"}`},
+		{"nil", nil, "{}"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := toPGArray(c.tags)
+			if got != c.want {
+				t.Errorf("toPGArray() = %q, want %q", got, c.want)
+			}
+		})
+	}
+
+	// Special chars: tags containing " or \ are NOT escaped by toPGArray.
+	// This is a latent bug — Postgres array literals require these to be
+	// backslash-escaped. Test documents current behavior so a fix is
+	// detectable. Should be fixed.
+	t.Run("special chars unescaped (current buggy behavior)", func(t *testing.T) {
+		got := toPGArray([]string{`a"b`, `c\d`})
+		// Current output: {"a"b","c\d"} — invalid Postgres array literal.
+		want := `{"a"b","c\d"}`
+		if got != want {
+			t.Errorf("toPGArray(special) = %q, want %q (if this changed, the escaping bug was fixed — update this test)", got, want)
+		}
+	})
+}