fix(cli): never create note-only content for an empty OpenCode 2 result

Tool.Result allows content: [], and for it the array branch of
appendResult pushed a text part that held only the session note, so the
note became the whole content of the tool result. Add a text part only
when the array already holds a part; an empty array now falls through to
the string output branch, or the result is returned unchanged.

Pin it in a new agent_clients test: the part-adding push sits inside the
non-empty array branch, ahead of the string output fallback, and no
unguarded array branch is left.

Refs #2204

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

src/cli/client_adapter.c

@@ -491,14 +491,18 @@ char *cbm_client_adapter_opencode(const char *binary_path) {
      * string/parts surface the model reads, output is the tool's schema-typed
      * value). Append to content first, then a string output; if neither text
      * surface exists, leave the result untouched so the tool's own output is
-     * never hidden. The caller assigns the returned result onto event.result. */
+     * never hidden. A parts array gets a new text part only when it already
+     * holds a part: `content: []` is a valid result, and a part added there
+     * would be the note alone, so an empty array falls through to the string
+     * output (or the unchanged result). The caller assigns the returned result
+     * onto event.result. */
     sb_append(&sb,
               "function appendResult(result, extra) {\n"
               "  if (!result || typeof result !== 'object') return result;\n"
               "  if (typeof result.content === 'string') {\n"
               "    return { ...result, content: result.content + '\\n' + extra };\n"
               "  }\n"
-              "  if (Array.isArray(result.content)) {\n"
+              "  if (Array.isArray(result.content) && result.content.length > 0) {\n"
               "    const content = result.content.slice();\n"
               "    for (let i = content.length - 1; i >= 0; i--) {\n"
               "      if (content[i] && content[i].type === 'text') {\n"

tests/test_agent_clients.c

@@ -1432,6 +1432,31 @@ TEST(client_adapter_opencode_v2_compaction_note_goes_into_the_compaction_message
     PASS();
 }
 
+/* #2204: Tool.Result allows `content: []`. appendResult adds a text part to a
+ * parts array only when the array already holds a part; an empty array falls
+ * through to the string `output` (or the unchanged result), so the note never
+ * becomes the whole content of a tool result. */
+TEST(client_adapter_opencode_v2_append_result_never_creates_note_only_content) {
+    char *js = cbm_client_adapter_opencode("/usr/local/bin/codebase-memory-mcp");
+    ASSERT_NOT_NULL(js);
+    const char *parts =
+        strstr(js, "if (Array.isArray(result.content) && result.content.length > 0) {");
+    const char *add_part = strstr(js, "content.push({ type: 'text', text: extra });");
+    const char *output_fallback = strstr(js, "if (typeof result.output === 'string') {");
+    ASSERT_NOT_NULL(parts);
+    ASSERT_NOT_NULL(add_part);
+    ASSERT_NOT_NULL(output_fallback);
+    /* The only part-adding push sits inside the non-empty branch; the string
+     * output fallback, where `content: []` lands, comes after it. */
+    ASSERT_TRUE(parts < add_part);
+    ASSERT_TRUE(add_part < output_fallback);
+    ASSERT_NULL(strstr(add_part + 1, "content.push("));
+    /* No unguarded array branch is left. */
+    ASSERT_NULL(strstr(js, "if (Array.isArray(result.content)) {"));
+    free(js);
+    PASS();
+}
+
 /* augment() is awaited inline inside 'tool.execute.after', so a hook-augment
  * that never exits would stall every grep/glob/read completion in the host
  * session until the agent is restarted. The generated plugin must bound the
@@ -1505,6 +1530,7 @@ SUITE(agent_clients) {
     RUN_TEST(client_adapter_opencode_covers_lifecycle_read_and_compaction);
     RUN_TEST(client_adapter_opencode_exports_the_v2_default_definition_issue2077);
     RUN_TEST(client_adapter_opencode_v2_compaction_note_goes_into_the_compaction_messages);
+    RUN_TEST(client_adapter_opencode_v2_append_result_never_creates_note_only_content);
     RUN_TEST(client_adapter_opencode_bounds_a_hung_hook_augment_child);
     RUN_TEST(client_adapter_rejects_missing_binary_path);
 }