P1-34: e2e smoke runbook + redacted GET /repo-credentials

Adds docs/e2e-smoke.md — an ~5-minute runbook that walks the full
P1 happy path against a sibling restic/rest-server: bootstrap
admin, mint token with repo creds, enrol an agent, watch the
config.update push land, run a backup, confirm the snapshot, edit
creds and watch the second push fire. Per the design discussion
this is a runbook (not a Go integration test); the Playwright
version lands in P5-06.

GET /api/hosts/{id}/repo-credentials returns the redacted view —
{repo_url, repo_username, has_password} — so the UI can pre-fill
the edit form without ever pulling the password out of the AEAD
blob.

Marks P1-32 / P1-33 / P1-34 done in tasks.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/server/http/host_credentials.go

@@ -18,6 +18,53 @@ import (
 
 func nowUTC() time.Time { return time.Now().UTC() }
 
+// hostRepoCredsView is the body of GET /api/hosts/{id}/repo-credentials.
+// Password is always redacted; the UI uses this to pre-fill an edit
+// form with the URL/username already populated.
+type hostRepoCredsView struct {
+	RepoURL      string `json:"repo_url"`
+	RepoUsername string `json:"repo_username,omitempty"`
+	HasPassword  bool   `json:"has_password"`
+}
+
+// handleGetHostCredentials returns a redacted view of the host's repo
+// creds for UI display. 404 if no credential has ever been set.
+func (s *Server) handleGetHostCredentials(w stdhttp.ResponseWriter, r *stdhttp.Request) {
+	if !s.authedUser(r) {
+		writeJSONError(w, stdhttp.StatusUnauthorized, "unauthorized", "")
+		return
+	}
+	hostID := chi.URLParam(r, "id")
+	if hostID == "" {
+		writeJSONError(w, stdhttp.StatusBadRequest, "missing_id", "")
+		return
+	}
+	enc, err := s.deps.Store.GetHostCredentials(r.Context(), hostID)
+	if err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			writeJSONError(w, stdhttp.StatusNotFound, "not_set", "")
+			return
+		}
+		writeJSONError(w, stdhttp.StatusInternalServerError, "internal", "")
+		return
+	}
+	plain, err := s.deps.AEAD.Decrypt(enc, []byte("host:"+hostID))
+	if err != nil {
+		writeJSONError(w, stdhttp.StatusInternalServerError, "decrypt_failed", "")
+		return
+	}
+	var blob repoCredsBlob
+	if err := json.Unmarshal(plain, &blob); err != nil {
+		writeJSONError(w, stdhttp.StatusInternalServerError, "internal", "")
+		return
+	}
+	writeJSON(w, stdhttp.StatusOK, hostRepoCredsView{
+		RepoURL:      blob.RepoURL,
+		RepoUsername: blob.RepoUsername,
+		HasPassword:  blob.RepoPassword != "",
+	})
+}
+
 // hostRepoCredsRequest is the body of PUT /api/hosts/{id}/repo-credentials.
 // Operator can edit any subset; missing fields preserve the existing
 // value (so changing only the password doesn't require resending the URL).