fix: stop artifact uploads depending on the cache server reaching Gitea (#1216)

Cache v2 makes the cache server the `ACTIONS_RESULTS_URL` origin, so artifact calls arrived there and were proxied on to Gitea, failing whenever it could not reach the instance.

- Artifact calls are answered with a redirect, so the cache server opens no connection to Gitea. A scheme change or an untrusted instance is still proxied, but there the cache server is the runner itself, which already reaches Gitea.
- Failures answer in twirp, not an empty `502` that clients report as `Unexpected end of JSON input`.
- `cache.v2: false` really points artifacts at Gitea now.
- Cache reservations are bound to the job that made them, so two jobs saving one key cannot commit against each other's upload, and a retry after a lost answer no longer fails a saved entry.
- The toolkit patch, which edits the GitHub-host check out of an action's bundle, was left in the shared checkout where a job running with `runner.patch_actions: false` could inherit it. It is put back after the job's copy.
- `exec` names an origin for the cache v2 it advertises, and masks its runtime token.

Behaviour changes: `no_proxy` no longer exempts `cache.external_server`, and `cache.enabled: false` also stops external registration.

Fixes https://gitea.com/gitea/runner/issues/1208
Fixes https://gitea.com/gitea/runner/issues/1211

Assisted by Claude (Opus 5).

Reviewed-on: https://gitea.com/gitea/runner/pulls/1216
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/artifactcache/handler.go

@@ -603,12 +603,12 @@ func (h *Handler) bearerAuth(handler httprouter.Handle) httprouter.Handle {
 		h.logger.Debugf("%s %s", r.Method, r.URL.Path)
 		token := bearerToken(r)
 		if token == "" {
-			h.responseJSON(w, r, http.StatusUnauthorized, errors.New("missing bearer token"))
+			h.unauthorized(w, r, errors.New("missing bearer token"))
 			return
 		}
 		cred, ok := h.lookupCredential(token)
 		if !ok {
-			h.responseJSON(w, r, http.StatusUnauthorized, errors.New("unknown bearer token"))
+			h.unauthorized(w, r, errors.New("unknown bearer token"))
 			return
 		}
 		ctx := context.WithValue(r.Context(), credKey{}, cred)
@@ -617,6 +617,14 @@ func (h *Handler) bearerAuth(handler httprouter.Handle) httprouter.Handle {
 	}
 }
 
+func (h *Handler) unauthorized(w http.ResponseWriter, r *http.Request, err error) {
+	if strings.HasPrefix(r.URL.Path, cacheServiceV2Path) {
+		h.twirpError(w, r, twirpUnauthenticated, err)
+		return
+	}
+	h.responseJSON(w, r, http.StatusUnauthorized, err)
+}
+
 // signedAuth authenticates a signed URL. purpose separates the flavours of URL the
 // handler hands out, so one cannot be replayed as another; see computeSignature.
 func (h *Handler) signedAuth(purpose string, handler httprouter.Handle) httprouter.Handle {
@@ -720,6 +728,12 @@ func (h *Handler) internalRevoke(w http.ResponseWriter, r *http.Request, _ httpr
 	h.responseJSON(w, r, http.StatusOK)
 }
 
+// hashedToken fingerprints a job's bearer, so a reservation can tell its own retry from another job.
+func hashedToken(token string) string {
+	sum := sha256.Sum256([]byte(token))
+	return hex.EncodeToString(sum[:])
+}
+
 func bearerToken(r *http.Request) string {
 	auth := r.Header.Get("Authorization")
 	const prefix = "Bearer "
@@ -805,8 +819,8 @@ func findExactCache(db *bolthold.Store, repo, key, version string, complete bool
 	}
 	cache := &Cache{}
 	err := db.FindOne(cache,
-		bolthold.Where("Repo").Eq(repo).
-			And("Key").Eq(key).
+		bolthold.Where("Key").Eq(key).Index("Key").
+			And("Repo").Eq(repo).
 			And("Version").Eq(version).
 			And("Complete").Eq(complete).
 			SortBy(sortBy).Reverse())