Rotate a database target's archive monthly, daily or hourly (closes #379)

A database target's rotation (none, monthly, daily or hourly) puts the
UTC period of each event's receive time in its archive file name, so
each file holds exactly its period's events. It is on the new webhook
page, the add target form and the target edit form, and shown in the
target list.

Renames move every one of a target's files and move them back if one
fails. The sweep prunes every file, one at a time under the target's
lock, and deletes a rotated file it leaves empty. Download lists the
files, then opens one at a time, oldest first, finding each again under
the target's current names, and gives each row its period. The target
list names the current file and totals the size of all of them.

Model: opus-5-5

internal/handlers/handlers_test.go

@@ -477,23 +477,37 @@ func TestRenderTemplateMidRenderErrorSendsNoPartialBody(t *testing.T) {
 func TestBuildDatabaseTargetConfig_Valid(t *testing.T) {
 	t.Parallel()
 
-	// Empty expiry: the keep-forever default, empty config.
-	cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest("")
+	// Empty expiry and rotation: the keep-forever, one-file default,
+	// empty config.
+	cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest("", "")
 	require.NoError(t, err)
 	assert.Empty(t, errMsg)
 	assert.Empty(t, cfg)
 
 	// Explicit never is stored as config.
-	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("never")
+	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("never", "")
 	require.NoError(t, err)
 	assert.Empty(t, errMsg)
 	assert.JSONEq(t, `{"expiry":"never"}`, cfg)
 
 	// A positive duration is stored as config.
-	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("720h")
+	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("720h", "")
 	require.NoError(t, err)
 	assert.Empty(t, errMsg)
 	assert.JSONEq(t, `{"expiry":"720h"}`, cfg)
+
+	// A rotation is stored as config, with or without an expiry.
+	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("", "daily")
+	require.NoError(t, err)
+	assert.Empty(t, errMsg)
+	assert.JSONEq(t, `{"rotation":"daily"}`, cfg)
+
+	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest(
+		"720h", "hourly",
+	)
+	require.NoError(t, err)
+	assert.Empty(t, errMsg)
+	assert.JSONEq(t, `{"expiry":"720h","rotation":"hourly"}`, cfg)
 }
 
 func TestBuildDatabaseTargetConfig_RejectsBadExpiry(
@@ -502,7 +516,7 @@ func TestBuildDatabaseTargetConfig_RejectsBadExpiry(
 	t.Parallel()
 
 	for _, bad := range []string{"nonsense", "7d", "-5h"} {
-		cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest(bad)
+		cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest(bad, "")
 
 		require.NoError(t, err)
 		assert.Contains(
@@ -512,3 +526,20 @@ func TestBuildDatabaseTargetConfig_RejectsBadExpiry(
 		assert.Empty(t, cfg)
 	}
 }
+
+func TestBuildDatabaseTargetConfig_RejectsBadRotation(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	for _, bad := range []string{"weekly", "Daily", " none"} {
+		cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest("", bad)
+
+		require.NoError(t, err)
+		assert.Contains(
+			t, errMsg, "Invalid archive rotation",
+			"rotation %q should be refused", bad,
+		)
+		assert.Empty(t, cfg)
+	}
+}