Store a target's settings as columns (closes #543)

A target's settings move from the per-type JSON string in
targets.config to columns: url, headers, timeout_seconds,
forward_query, archive_expiry and archive_rotation. A column a type
does not use stays empty. headers holds the header map as JSON text
through GORM's JSON serializer, and archive_expiry holds a
time.Duration, 0 meaning never. The forms check each setting once,
with the same refusals and messages, and the edit form is filled from
the columns, so the per-type config structs, their parsers and the
"could not be read" branches are gone. A delivery task carries the
six settings in place of the JSON string; tests check that each copy
into a task, and back out of one, keeps all six.

Model: opus-5-5

internal/delivery/target_slack.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -15,18 +14,6 @@ import (
 	"sneak.berlin/go/webhooker/internal/database"
 )
 
-// errMissingWebhookURL is returned when a Slack target config
-// omits its webhook URL.
-var errMissingWebhookURL = errors.New(
-	"webhook_url is required",
-)
-
-// SlackTargetConfig holds configuration for slack target
-// types.
-type SlackTargetConfig struct {
-	WebhookURL string `json:"webhookUrl"`
-}
-
 // slackTarget delivers events to Slack incoming webhooks. It
 // formats the event into a Slack message and posts it as
 // JSON. It shares the retry core with the HTTP target: a
@@ -46,19 +33,6 @@ func (t *slackTarget) Deliver(
 	task *Task,
 	sched Scheduler,
 ) {
-	cfg, err := parseSlackConfig(d.Target.Config)
-	if err != nil {
-		t.eng.log.Error(
-			"invalid Slack target config",
-			"target_id", d.TargetID,
-			"error", err,
-		)
-
-		t.failConfig(webhookDB, d, err)
-
-		return
-	}
-
 	msg := FormatSlackMessage(&d.Event)
 
 	payload, err := json.Marshal(
@@ -71,13 +45,26 @@ func (t *slackTarget) Deliver(
 			"error", err,
 		)
 
-		t.failConfig(webhookDB, d, err)
+		recErr := t.eng.recordResult(
+			webhookDB, d, 1,
+			false, 0, "", err.Error(), 0,
+		)
+		if recErr != nil {
+			t.eng.bookkeepingFailed(d, recErr)
+
+			return
+		}
+
+		t.eng.settleStatus(
+			webhookDB, d, d.Target.Type,
+			database.DeliveryStatusFailed,
+		)
 
 		return
 	}
 
 	attempt := func() attemptResult {
-		return t.attempt(ctx, cfg, payload)
+		return t.attempt(ctx, d.Target.URL, payload)
 	}
 
 	t.deliver(
@@ -86,37 +73,13 @@ func (t *slackTarget) Deliver(
 	)
 }
 
-// failConfig records a first-attempt failure for a delivery
-// that could not be prepared (bad config or unmarshalable
-// payload) and marks it failed.
-func (t *slackTarget) failConfig(
-	webhookDB *gorm.DB,
-	d *database.Delivery,
-	err error,
-) {
-	recErr := t.eng.recordResult(
-		webhookDB, d, 1,
-		false, 0, "", err.Error(), 0,
-	)
-	if recErr != nil {
-		t.eng.bookkeepingFailed(d, recErr)
-
-		return
-	}
-
-	t.eng.settleStatus(
-		webhookDB, d, d.Target.Type,
-		database.DeliveryStatusFailed,
-	)
-}
-
-// attempt performs a single Slack POST and derives its
-// outcome, preserving the engine's original semantics: a
+// attempt performs a single Slack POST to targetURL and derives
+// its outcome, preserving the engine's original semantics: a
 // non-2xx response records an "HTTP <code>" error string and
 // a transport error records a "sending request" error.
 func (t *slackTarget) attempt(
 	ctx context.Context,
-	cfg *SlackTargetConfig,
+	targetURL string,
 	payload []byte,
 ) attemptResult {
 	start := time.Now()
@@ -124,7 +87,7 @@ func (t *slackTarget) attempt(
 	req, err := http.NewRequestWithContext(
 		ctx,
 		http.MethodPost,
-		cfg.WebhookURL,
+		targetURL,
 		bytes.NewReader(payload),
 	)
 	if err != nil {
@@ -186,31 +149,6 @@ func (t *slackTarget) readSlackResponse(
 	}
 }
 
-func parseSlackConfig(
-	configJSON string,
-) (*SlackTargetConfig, error) {
-	if configJSON == "" {
-		return nil, errEmptyTargetConfig
-	}
-
-	var cfg SlackTargetConfig
-
-	err := json.Unmarshal(
-		[]byte(configJSON), &cfg,
-	)
-	if err != nil {
-		return nil, fmt.Errorf(
-			"parsing config JSON: %w", err,
-		)
-	}
-
-	if cfg.WebhookURL == "" {
-		return nil, errMissingWebhookURL
-	}
-
-	return &cfg, nil
-}
-
 // FormatSlackMessage builds a Slack-compatible message
 // string from a webhook event.
 func FormatSlackMessage(