diff --git a/tools/omnivoice/CMakeLists.txt b/tools/omnivoice/CMakeLists.txt
index 2be48b753..ec56da599 100644
--- a/tools/omnivoice/CMakeLists.txt
+++ b/tools/omnivoice/CMakeLists.txt
@@ -369,7 +369,7 @@ if(TARGET mtmd)
     endif()
     add_dependencies(elizainference_static omnivoice-version)
 
-    # FFI tests (ABI v17).
+    # FFI tests (ABI v18).
     #   eliza-inference-test-abi      links the real libelizainference: ABI
     #                                 string, probes, cancel/evict no-ops, and
     #                                 (opt-in, ELIZA_TEST_ASR_DIR) a real-model
diff --git a/tools/omnivoice/include/eliza-inference-ffi.h b/tools/omnivoice/include/eliza-inference-ffi.h
index d00f0d2d7..b7b31a79d 100644
--- a/tools/omnivoice/include/eliza-inference-ffi.h
+++ b/tools/omnivoice/include/eliza-inference-ffi.h
@@ -1,5 +1,5 @@
 /*
- * libelizainference FFI ABI v17.
+ * libelizainference FFI ABI v18.
  *
  * (Banner tracks ELIZA_INFERENCE_ABI_VERSION below; the per-version history is
  * at the end of this header preamble, newest first.)
@@ -134,6 +134,16 @@ extern "C" {
  * load and refuses to bind if they disagree.
  *
  * Changelog:
+ *   v18: text-model context capacity resolved before stream admission.
+ *         - `eliza_inference_llm_context_capacity(ctx, requested_context,
+ *           n_gpu_layers, &out_capacity, &err)` loads the resident text model
+ *           (if needed) and returns the context size `llm_stream_open` would
+ *           use: `requested_context`, else ELIZA_LLM_N_CTX, else 8192, clamped
+ *           to the GGUF training context. No decode context is allocated.
+ *         - `llm_stream_open` now shares that resolution and rejects a
+ *           non-positive capacity instead of creating a zero-sized context.
+ *       Additive symbol; no existing signature changes. A v17 library lacks
+ *       the symbol, so loaders must treat it as absent.
  *   v17: Paradee-8M TTS with native misaki G2P, plus cancellation and
  *       eviction for every TTS head and for ASR. All additions are new
  *       symbols; no existing signature changes.
@@ -254,9 +264,9 @@ extern "C" {
  *   v7: real Silero VAD (same symbol surface as v6).
  *   v6: fused wake-word, speaker, diarizer.
  */
-#define ELIZA_INFERENCE_ABI_VERSION 17
+#define ELIZA_INFERENCE_ABI_VERSION 18
 
-/* Returns a static, NUL-terminated string of the form "17" matching
+/* Returns a static, NUL-terminated string of the form "18" matching
  * ELIZA_INFERENCE_ABI_VERSION at the time the library was built. The
  * pointer is owned by the library — do NOT free. */
 const char * eliza_inference_abi_version(void);
@@ -1152,6 +1162,19 @@ typedef struct {
 /* Opaque streaming-LLM session. One per active generation. */
 typedef struct EliLlmStream EliLlmStream;
 
+/* Resolve the streaming context capacity against the resident text model
+ * before token admission (ABI v18). Loads the model with n_gpu_layers when
+ * necessary. requested_context <=0 uses ELIZA_LLM_N_CTX or 8192; the result
+ * is clamped to the GGUF training context exactly as stream_open does.
+ * On success, pass *out_capacity explicitly to stream_open to preserve this
+ * decision even if the environment changes. No decode context is allocated. */
+int eliza_inference_llm_context_capacity(
+    EliInferenceContext * ctx,
+    int32_t requested_context,
+    int32_t n_gpu_layers,
+    int32_t * out_capacity,
+    char ** out_error);
+
 /* Open a session anchored to `ctx`. Loads the bundle's text GGUF on first
  * open and reuses it across sessions. Returns NULL on failure with
  * `*out_error` populated. Close exactly once via `_close`. */
diff --git a/tools/omnivoice/src/eliza-inference-ffi.cpp b/tools/omnivoice/src/eliza-inference-ffi.cpp
index 8ec811696..7a390126a 100644
--- a/tools/omnivoice/src/eliza-inference-ffi.cpp
+++ b/tools/omnivoice/src/eliza-inference-ffi.cpp
@@ -3796,6 +3796,40 @@ int eliza_inference_llm_kv_quant_supported(void) {
     return 1;
 }
 
+static int eliza_llm_context_capacity(
+    const llama_model * model, int32_t requested_context) {
+    const int n_ctx_train = llama_model_n_ctx_train(model);
+    int n_ctx = requested_context > 0
+        ? requested_context
+        : eliza_int_env_or_default("ELIZA_LLM_N_CTX", 8192);
+    if (n_ctx_train > 0 && n_ctx > n_ctx_train) n_ctx = n_ctx_train;
+    return n_ctx;
+}
+
+int eliza_inference_llm_context_capacity(
+    EliInferenceContext * ctx,
+    int32_t requested_context,
+    int32_t n_gpu_layers,
+    int32_t * out_capacity,
+    char ** out_error) {
+    if (!ctx || !out_capacity) {
+        eliza_set_error(out_error,
+            "[libelizainference] llm_context_capacity: ctx and out_capacity are required");
+        return ELIZA_ERR_INVALID_ARG;
+    }
+    std::lock_guard<std::mutex> lock(ctx->llm_mutex);
+    const int rc = eliza_load_llm_model_locked(ctx, n_gpu_layers, out_error);
+    if (rc != ELIZA_OK) return rc;
+    const int capacity = eliza_llm_context_capacity(ctx->llm_model, requested_context);
+    if (capacity <= 0) {
+        eliza_set_error(out_error,
+            "[libelizainference] llm_context_capacity: context capacity must be positive");
+        return ELIZA_ERR_INVALID_ARG;
+    }
+    *out_capacity = capacity;
+    return ELIZA_OK;
+}
+
 EliLlmStream * eliza_inference_llm_stream_open(
     EliInferenceContext * ctx,
     const eliza_llm_stream_config_t * cfg,
@@ -3827,11 +3861,13 @@ EliLlmStream * eliza_inference_llm_stream_open(
      * MTP engine's target context so both decode identically (same n_ctx /
      * batch / threads / flash-attn / KV-quant). */
     llama_context_params cparams = llama_context_default_params();
-    const int n_ctx_train = llama_model_n_ctx_train(model);
-    int n_ctx = cfg->context_size > 0
-        ? cfg->context_size
-        : eliza_int_env_or_default("ELIZA_LLM_N_CTX", 8192);
-    if (n_ctx_train > 0 && n_ctx > n_ctx_train) n_ctx = n_ctx_train;
+    const int n_ctx = eliza_llm_context_capacity(model, cfg->context_size);
+    if (n_ctx <= 0) {
+        eliza_set_error(out_error,
+            "[libelizainference] llm_stream_open: context capacity must be positive");
+        delete stream;
+        return nullptr;
+    }
     cparams.n_ctx = (uint32_t) n_ctx;
     cparams.n_batch = (uint32_t) eliza_int_env_or_default("ELIZA_LLM_N_BATCH", 512);
     cparams.n_ubatch = cparams.n_batch;
diff --git a/tools/omnivoice/tests/ffi-abi.c b/tools/omnivoice/tests/ffi-abi.c
index 03c997b45..8dd147450 100644
--- a/tools/omnivoice/tests/ffi-abi.c
+++ b/tools/omnivoice/tests/ffi-abi.c
@@ -1,7 +1,8 @@
 /* tools/omnivoice/tests/ffi-abi.c
  *
- * C11 test against the real libelizainference (ABI v17). Always runs:
- *   - ABI string "17" and the v17 capability probes
+ * C11 test against the real libelizainference (ABI v18). Always runs:
+ *   - ABI string "18" and the v17 capability probes
+ *   - v18 llm_context_capacity argument validation and the no-text-GGUF error
  *   - cancel_tts / asr_cancel are no-ops with nothing in flight
  *   - mmap_evict / mmap_acquire("tts") on a bundle with no TTS weights
  *   - Paradee entries before any load (or NOT_IMPLEMENTED when not built)
@@ -49,7 +50,7 @@ static double now_ms(void) {
 
 static void test_probes_and_noops(void) {
     char * err = NULL;
-    CHECK(strcmp(eliza_inference_abi_version(), "17") == 0);
+    CHECK(strcmp(eliza_inference_abi_version(), "18") == 0);
     CHECK_RC(eliza_inference_asr_supported(), 1);
 #if defined(ELIZA_TEST_EXPECT_PARADEE)
     CHECK_RC(eliza_inference_paradee_supported(), 1);
@@ -72,6 +73,18 @@ static void test_probes_and_noops(void) {
     clear_err(&err);
     CHECK_RC(eliza_inference_mmap_evict(ctx, "tts", &err), ELIZA_OK);
     CHECK_RC(eliza_inference_mmap_evict(ctx, "asr", &err), ELIZA_OK);
+    /* v18: capacity resolution validates its arguments and reports a bundle
+     * without a text GGUF instead of returning a capacity. */
+    int32_t capacity = -12345;
+    CHECK_RC(eliza_inference_llm_context_capacity(NULL, 0, 0, &capacity, &err), ELIZA_ERR_INVALID_ARG);
+    CHECK(capacity == -12345);
+    clear_err(&err);
+    CHECK_RC(eliza_inference_llm_context_capacity(ctx, 0, 0, NULL, &err), ELIZA_ERR_INVALID_ARG);
+    clear_err(&err);
+    CHECK_RC(eliza_inference_llm_context_capacity(ctx, 4096, 0, &capacity, &err), ELIZA_ERR_BUNDLE_INVALID);
+    CHECK(capacity == -12345);
+    CHECK(err != NULL);
+    clear_err(&err);
     /* No TTS weights and no configured Kokoro/Paradee head. */
     CHECK_RC(eliza_inference_mmap_acquire(ctx, "tts", &err), ELIZA_ERR_BUNDLE_INVALID);
     clear_err(&err);
diff --git a/tools/omnivoice/tests/ffi-paradee-asr.cpp b/tools/omnivoice/tests/ffi-paradee-asr.cpp
index 28c95c3fd..33b85834e 100644
--- a/tools/omnivoice/tests/ffi-paradee-asr.cpp
+++ b/tools/omnivoice/tests/ffi-paradee-asr.cpp
@@ -9,7 +9,7 @@
 //   - eliza_inference_asr_cancel during prefill and during decode, over a
 //     scripted ASR engine that polls the same abort callback llama_decode
 //     uses
-//   - ABI string "17"
+//   - ABI string "18"
 //
 // The bridge is compiled into this TU (ELIZA_INFERENCE_TEST_HOOKS) against
 // the Paradee / misaki doubles in tests/paradee-contract/, so no weights are
@@ -86,7 +86,7 @@ static int synth_text(EliInferenceContext * ctx, const std::string & text, size_
 }
 
 static void test_abi_and_probes() {
-    CHECK(std::string(eliza_inference_abi_version()) == "17");
+    CHECK(std::string(eliza_inference_abi_version()) == "18");
     CHECK_RC(eliza_inference_paradee_supported(), 1);
     CHECK_RC(eliza_inference_asr_supported(), 1);
     CHECK_RC(eliza_inference_asr_stream_supported(), 0);