Store a target's number of delivery attempts, at least one (closes #540)

Target.MaxRetries (max_retries) becomes Target.MaxAttempts
(max_attempts), and the form field, parser and ceiling are renamed to
match. The column is NOT NULL and a check constraint refuses a value
below 1, so every target, whatever its type, is stored with at least
1. 1 is a single attempt with no circuit breaker; above 1 retries
behind the breaker up to that many attempts. Both target forms refuse
0 and less; a blank field on the add target form gives 1, and on the
edit form keeps the stored value. The target page shows the plain
number, and the README's two paragraphs on 0 against 1 become one
sentence.

Model: opus-5-5

internal/handlers/ui_copy_test.go

@@ -348,21 +348,19 @@ func TestEntrypointCopyButtonIsProgressiveEnhancement(t *testing.T) {
 	)
 }
 
-// maxRetriesHelp is the wording both target forms must carry. The
-// delivery core makes max_retries attempts in total, not that many
+// maxAttemptsHelp is the wording both target forms must carry. The
+// delivery core makes max_attempts attempts in total, not that many
 // retries on top of a first try (a fresh delivery starts at attempt 1
 // and target_http gives up once the attempt number reaches
-// max_retries), and 0 is special-cased to a single fire-and-forget
-// attempt with no circuit breaker.
-const maxRetriesHelp = "How many times each delivery is attempted in " +
-	"all, the first attempt included. 0 means a single attempt with no " +
-	"retries and no circuit breaker."
+// max_attempts).
+const maxAttemptsHelp = "How many times each delivery is attempted in " +
+	"all, the first attempt included."
 
-// TestTargetFormMaxRetriesCopyMatchesBehaviour pins the max_retries
+// TestTargetFormMaxAttemptsCopyMatchesBehaviour pins the max_attempts
 // label, "Delivery attempts", and help text on both the create form
 // (the add-target form on the webhook detail page) and the edit form,
 // so the copy cannot drift back to calling the number a retry count.
-func TestTargetFormMaxRetriesCopyMatchesBehaviour(t *testing.T) {
+func TestTargetFormMaxAttemptsCopyMatchesBehaviour(t *testing.T) {
 	t.Parallel()
 
 	var h *handlers.Handlers
@@ -394,11 +392,11 @@ func TestTargetFormMaxRetriesCopyMatchesBehaviour(t *testing.T) {
 
 	assert.Contains(t, createBody, "Delivery attempts:</label>")
 	assert.Contains(
-		t, createBody, maxRetriesHelp,
-		"the add-target form must explain max_retries as total attempts",
+		t, createBody, maxAttemptsHelp,
+		"the add-target form must explain max_attempts as total attempts",
 	)
 
-	// A slack target exercises the same max_retries field while needing
+	// A slack target exercises the same max_attempts field while needing
 	// only a URL from the edit template, so the test data stays
 	// minimal. The Target and TargetForm keys mirror the field names
 	// the template reads off the handler's values.
@@ -412,8 +410,8 @@ func TestTargetFormMaxRetriesCopyMatchesBehaviour(t *testing.T) {
 				"Active": true,
 			},
 			"TargetForm": map[string]any{
-				"URL":        "https://hooks.slack.com/services/x",
-				"MaxRetries": "3",
+				"URL":         "https://hooks.slack.com/services/x",
+				"MaxAttempts": "3",
 			},
 			dataKeyError: "",
 		},
@@ -421,8 +419,8 @@ func TestTargetFormMaxRetriesCopyMatchesBehaviour(t *testing.T) {
 
 	assert.Contains(t, editBody, `class="label">Delivery attempts</label>`)
 	assert.Contains(
-		t, editBody, maxRetriesHelp,
-		"the target edit form must explain max_retries as total attempts",
+		t, editBody, maxAttemptsHelp,
+		"the target edit form must explain max_attempts as total attempts",
 	)
 }