Make delivery and integration failures explicit

Persist reminder presentations and retry state, atomically complete collapsed deliveries, fall back across away reaches, and block permanent failures visibly (V-715, V-678). Fail closed when enabled integrations lack credentials and keep remote arms explicitly dark (V-691). Give mavweb one sanitized, request-correlated error contract (V-689). Owner explicitly requested direct commits to master.

cmd/mavweb/ambient.go

@@ -4,6 +4,7 @@ import (
 	"crypto/subtle"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"log"
 	"net/http"
@@ -51,34 +52,41 @@ type ambientResp struct {
 // never registered, so it is treated as a hard failure here too.
 func handleAmbient(w http.ResponseWriter, r *http.Request, core ipc.CoreAPI, token string) {
 	if r.Method != http.MethodPost {
-		http.Error(w, "POST only", http.StatusMethodNotAllowed)
+		writeProblem(w, r, http.StatusMethodNotAllowed, problemMethodNotAllowed,
+			"POST only", nil)
 		return
 	}
 	if token == "" {
-		http.Error(w, "ambient ingest disabled (no -ambient-token)", http.StatusServiceUnavailable)
+		writeProblem(w, r, http.StatusServiceUnavailable, problemIntegrationOff,
+			"ambient ingest disabled (no -ambient-token)", nil)
 		return
 	}
 	if !ambientAuthorized(r, token) {
-		http.Error(w, "unauthorized", http.StatusUnauthorized)
+		writeProblem(w, r, http.StatusUnauthorized, problemUnauthorized,
+			"unauthorized", nil)
 		return
 	}
 	if core == nil {
-		http.Error(w, "ambient ingest disabled (no -core)", http.StatusServiceUnavailable)
+		writeProblem(w, r, http.StatusServiceUnavailable, problemCoreUnavailable,
+			"ambient ingest disabled (no -core)", nil)
 		return
 	}
 
 	var n calendar.Notification
 	body, err := io.ReadAll(io.LimitReader(r.Body, ambientMaxBody))
 	if err != nil {
-		http.Error(w, "read failed", http.StatusBadRequest)
+		writeProblem(w, r, http.StatusBadRequest, problemInvalidRequest,
+			"read failed", fmt.Errorf("read ambient request: %w", err))
 		return
 	}
 	if err := json.Unmarshal(body, &n); err != nil {
-		http.Error(w, "bad json", http.StatusBadRequest)
+		writeProblem(w, r, http.StatusBadRequest, problemInvalidRequest,
+			"bad json", fmt.Errorf("decode ambient request: %w", err))
 		return
 	}
 	if n.Posted.IsZero() {
-		writeAmbient(w, http.StatusBadRequest, ambientResp{Reason: "posted_at is required"})
+		writeProblem(w, r, http.StatusBadRequest, problemInvalidRequest,
+			"posted_at is required", nil)
 		return
 	}
 
@@ -99,8 +107,8 @@ func handleAmbient(w http.ResponseWriter, r *http.Request, core ipc.CoreAPI, tok
 		writeAmbient(w, http.StatusOK, ambientResp{Stored: false, Key: key, Reason: "unchanged"})
 		return
 	} else if err != nil && !errors.Is(err, ipc.ErrNoFact) {
-		log.Printf("ambient: read %s: %v", key, err)
-		http.Error(w, "read failed", http.StatusBadGateway)
+		writeProblem(w, r, http.StatusBadGateway, problemCoreReadFailed,
+			"read failed", fmt.Errorf("read ambient fact %q: %w", key, err))
 		return
 	}
 
@@ -116,8 +124,8 @@ func handleAmbient(w http.ResponseWriter, r *http.Request, core ipc.CoreAPI, tok
 		Source:     calendar.SourceAmbient,
 		Confidence: calendar.AmbientConfidence,
 	}); err != nil {
-		log.Printf("ambient: write %s: %v", key, err)
-		http.Error(w, "write failed", http.StatusBadGateway)
+		writeProblem(w, r, http.StatusBadGateway, problemCoreWriteFailed,
+			"write failed", fmt.Errorf("write ambient fact %q: %w", key, err))
 		return
 	}
 	log.Printf("ambient: %s=%s (%s, pkg=%s)", key, val, calendar.SourceAmbient, n.Package)