diff --git a/epm/src/install.el b/epm/src/install.el
index 882fc90..1561cf8 100644
--- a/epm/src/install.el
+++ b/epm/src/install.el
@@ -17,6 +17,16 @@
 //   4. Append dep to order after all its transitive deps
 //   5. Deduplicate: skip already-ordered vessels
 
+// ── Cross-module forward declarations ─────────────────────────────────────────
+// Defined in sibling epm modules; resolved at link time. The `extern fn` decls
+// give elc the C prototypes so generated install.c compiles cleanly under strict
+// compilers (gcc>=14 / clang) that reject implicit function declarations.
+extern fn manifest_name(src: String) -> String                        // manifest.el
+extern fn manifest_deps(src: String) -> String                        // manifest.el
+extern fn registry_token() -> String                                  // registry.el
+extern fn registry_find(name: String, version: String) -> String     // registry.el
+extern fn registry_latest_version(name: String) -> String            // registry.el
+
 // ── Install paths ─────────────────────────────────────────────────────────────
 
 // packages_dir returns the root directory for installed vessels.
diff --git a/epm/src/registry.el b/epm/src/registry.el
index 8e1b2b5..d6f9730 100644
--- a/epm/src/registry.el
+++ b/epm/src/registry.el
@@ -14,6 +14,15 @@
 //   EPM_REGISTRY_ORG — org name that hosts vessel repos (default: neuron-technologies)
 //   EPM_TOKEN      — Gitea personal access token (required for publish)
 
+// ── Cross-module forward declarations ─────────────────────────────────────────
+// These symbols are defined in sibling epm modules or the El runtime and are
+// resolved at link time. The `extern fn` decls give elc the C prototype so the
+// generated registry.c compiles cleanly under strict compilers (gcc>=14 / clang)
+// that reject implicit function declarations. Signature arity must match the
+// definition; return/param types are informational (all lower to el_val_t).
+extern fn config(key: String) -> String          // El runtime builtin
+extern fn read_installed() -> String              // install.el
+
 // ── Config helpers ────────────────────────────────────────────────────────────
 
 // registry_api_url returns the Gitea API base URL with no trailing slash.
diff --git a/epm/src/update.el b/epm/src/update.el
index 42f60a5..3804ab2 100644
--- a/epm/src/update.el
+++ b/epm/src/update.el
@@ -6,6 +6,15 @@
 // Depends on: registry.el (registry_latest_version, registry_find),
 //             install.el  (read_installed, install_vessel, installed_version)
 
+// ── Cross-module forward declarations ─────────────────────────────────────────
+// Defined in sibling epm modules; resolved at link time. The `extern fn` decls
+// give elc the C prototypes so generated update.c compiles cleanly under strict
+// compilers (gcc>=14 / clang) that reject implicit function declarations.
+extern fn read_installed() -> String                                  // install.el
+extern fn installed_version(name: String) -> String                   // install.el
+extern fn install_vessel(name: String, version: String) -> Bool      // install.el
+extern fn registry_latest_version(name: String) -> String            // registry.el
+
 // ── Semver helpers ────────────────────────────────────────────────────────────
 
 // semver_part extracts the Nth dot-separated component from a semver string.