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. 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 and default a blank field to 1. 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",
 	)
 }