runtime: the link set is multi-file — name it once, ship all of it

el_runtime.c was created 2026-05-03 as an explicitly temporary build shim. It
was deleted that afternoon ("runtime is 100% native El") and restored 25 minutes
later "UNTIL the compiler is updated to emit #include el_seed.h". The `until`
never came. 3.5 months on it is 20,527 lines, and nothing was ever set up to
notice — a file scheduled for deletion gets no owner, no budget, no boundary.

What kept it growing is not inertia, it is an instruction. lang/AGENTS.md said
el_runtime.c "is the authoritative single-file link target ... THIS IS WHERE A
NEW C BUILTIN'S IMPLEMENTATION MUST CURRENTLY LIVE TO BE LINKABLE", and made it
step 1 of the add-a-builtin recipe. That is false. Placement is a link-time
concern: builtin_arity maps NAME -> ARITY INT only, the El name is emitted as
the exact C symbol, and `ld` resolves it — the compiler cannot tell which .c a
symbol came from. `nm lang/dist/platform/elc` on the shipped compiler already
shows T _engram_geo_reify_index_new, T _vindex_insert, T _engram_think,
T _engram_reason_abduce: it is linked from ten translation units today. In a
repo where agents write most of the code, a false instruction in the instruction
file is the forcing function. The file grew because the recipe said to grow it.

The multi-file runtime is therefore already real, and the docs and the
distribution never caught up — which left a live, shipped bug:

  * Linking el_runtime.c alone FAILS at `ld` (undefined engram_ground_json,
    engram_activate_inner, eg_find_relation, cog_assert_two_axis, ...) because
    el_runtime.c #includes six engram headers and calls into all six siblings.
  * sdk-release.yaml shipped el_runtime.c/.h + engram_store.c/.h and none of the
    other five required .c files, so downstream consumers of the el-runtime-c
    Artifact Registry package and of install.sh got a lib/ that cannot link.
  * .githooks/pre-commit linked el_runtime.c alone with stderr to /dev/null, so
    it reported all 13 native suites as FAILED with the real ld error invisible.
  * AGENTS.md's self-host recipe compiled el-compiler/runtime/el_runtime.c — a
    path the same file's "DO NOT EDIT" list names as a lagging fork.

The root fix is to stop writing the list down eight times:

  * lang/runtime/SOURCES — the canonical link set, in one place, in link order.
  * scripts/el-runtime-sources.sh — prints it, optionally prefixed; --check
    fails loudly on a missing file, --headers for the shipped headers.
  * Every link line in AGENTS.md, lang/AGENTS.md, DESIGN.md, lang/spec/language.md,
    the three workflows and the pre-commit hook now reads that one list.
  * Adding a concern's .c is one line in SOURCES, so a new builtin no longer has
    to be appended to el_runtime.c just because appending was the cheaper edit.

Distribution: ship the siblings rather than amalgamate. Amalgamation needs a new
tool and contradicts DESIGN.md's compile-once-link-many; the siblings are already
independently authored and independently tested (engram/test/*.sh link subsets
directly), and engram_store.c was already shipped, so this completes a mechanism
that existed rather than inventing one. Source is also a superset: a consumer
that wants one file can concatenate, one that wants separate TUs cannot undo an
amalgamation. el-runtime-c/-h stay for backward compatibility; el-runtime-src is
added carrying the complete set plus SOURCES.

lang/AGENTS.md now points new C builtins at the concern-owning .c and states
plainly that the compiler cannot tell which .c a symbol came from, with the nm
evidence. AGENTS.md's "reconcile which is canonical (verify)" note is resolved:
neither file supersedes the other, the canonical unit is the set.

Verified locally (the bar; not CI):
  * engram/src/server.el compiles and links against the SOURCES set.
  * Compile-once-link-many into libel.a links the same program.
  * elb builds from the corrected recipe.
  * Self-host fixpoint byte-identical (11,110 lines, stage2 == stage3) built
    with the SOURCES-driven link line.
  * pre-commit hook: 0 of 13 native suites passing -> 8 of 13.

The 5 still-failing suites are PRE-EXISTING and untouched here: test_fs
(fs_list_json undeclared), test_state (state_has, state_get_or undeclared),
test_json (json_build_array/json_build_object/json_escape_string undefined),
test_time (now_ns undefined), test_env (1 assertion). Builtins registered in
builtin_arity with no implementation or no declaration anywhere — the same
recipe defect, now visible because the linker error is no longer suppressed.

Not attempted: making elc emit #include el_seed.h and dropping elb's hardcoded
runtime path. That is the correct long-term fix and finishes the 2026-05-03
migration, but it touches codegen and self-hosting and belongs in its own change.

lang/install.sh

@@ -49,21 +49,47 @@ download() {
 TMP_DIR="$(mktemp -d)"
 trap 'rm -rf "${TMP_DIR}"' EXIT
 
-download "${RELEASE_BASE}/elc"          "${TMP_DIR}/elc"
-download "${RELEASE_BASE}/el_runtime.c" "${TMP_DIR}/el_runtime.c"
-download "${RELEASE_BASE}/el_runtime.h" "${TMP_DIR}/el_runtime.h"
+# The runtime is MULTI-FILE. el_runtime.c #includes six engram headers and makes
+# hard cross-TU calls into all six sibling .c files, so installing el_runtime.c
+# alone produces a lib/ that CANNOT LINK — `ld` fails with undefined
+# engram_ground_json / engram_activate_inner / eg_find_relation / cog_assert_two_axis.
+# This list mirrors lang/runtime/SOURCES (the in-repo source of truth); keep them
+# in step. install.sh is standalone by design — it runs on machines with no repo
+# checkout — so it cannot call scripts/el-runtime-sources.sh.
+RUNTIME_SOURCES=(
+    el_runtime.c el_seed.c
+    engram_store.c engram_vindex.c engram_geometry.c
+    engram_reason.c engram_verify.c engram_cognition.c
+    eg_cosine_batch.c eg_cosine_batch_strategy_cpu.c
+)
+RUNTIME_HEADERS=(
+    el_runtime.h el_seed.h
+    engram_store.h engram_vindex.h engram_geometry.h
+    engram_reason.h engram_verify.h engram_cognition.h
+    eg_cosine_batch.h eg_cosine_batch_strategy.h
+)
+
+download "${RELEASE_BASE}/elc" "${TMP_DIR}/elc"
+for f in "${RUNTIME_SOURCES[@]}" "${RUNTIME_HEADERS[@]}"; do
+    download "${RELEASE_BASE}/${f}" "${TMP_DIR}/${f}"
+done
 
 # Install
-install -m 755 "${TMP_DIR}/elc"          "${BIN_DIR}/elc"
-install -m 644 "${TMP_DIR}/el_runtime.c" "${LIB_DIR}/el_runtime.c"
-install -m 644 "${TMP_DIR}/el_runtime.h" "${LIB_DIR}/el_runtime.h"
+install -m 755 "${TMP_DIR}/elc" "${BIN_DIR}/elc"
+for f in "${RUNTIME_SOURCES[@]}" "${RUNTIME_HEADERS[@]}"; do
+    install -m 644 "${TMP_DIR}/${f}" "${LIB_DIR}/${f}"
+done
+
+# Record the link set so downstream Makefiles can read it instead of hardcoding.
+printf '%s\n' "${RUNTIME_SOURCES[@]}" > "${TMP_DIR}/SOURCES"
+install -m 644 "${TMP_DIR}/SOURCES" "${LIB_DIR}/SOURCES"
 
 echo
 echo "==> El SDK installed successfully"
 echo
 echo "    elc binary : ${BIN_DIR}/elc"
-echo "    runtime    : ${LIB_DIR}/el_runtime.c"
-echo "    header     : ${LIB_DIR}/el_runtime.h"
+echo "    runtime    : ${LIB_DIR}/ (${#RUNTIME_SOURCES[@]} .c files, ${#RUNTIME_HEADERS[@]} headers)"
+echo "    link set   : ${LIB_DIR}/SOURCES"
 echo
 echo "Add the following to your Makefile to build El programs:"
 echo
@@ -71,10 +97,14 @@ echo "    EL_LIB := ${LIB_DIR}"
 echo "    ELC    := elc"
 echo "    CC     := cc"
 echo "    CFLAGS := -std=c11 -O2 -I\$(EL_LIB)"
+echo "    LDLIBS := -lcurl -lssl -lcrypto -lpthread -lm"
+echo
+echo "    # The runtime is multi-file — link the whole set, not el_runtime.c alone."
+echo "    EL_RUNTIME := \$(addprefix \$(EL_LIB)/,\$(shell cat \$(EL_LIB)/SOURCES))"
 echo
 echo "    dist/myapp.c: src/myapp.el"
 echo "    \t\$(ELC) src/myapp.el > dist/myapp.c"
 echo
 echo "    dist/myapp: dist/myapp.c"
-echo "    \t\$(CC) \$(CFLAGS) -o dist/myapp dist/myapp.c \$(EL_LIB)/el_runtime.c -lcurl -lpthread"
+echo "    \t\$(CC) \$(CFLAGS) -o dist/myapp dist/myapp.c \$(EL_RUNTIME) \$(LDLIBS)"
 echo