@@ -524,6 +524,58 @@ static const char skill_content[] =
     "`direction=\"both\"`.\n"
     "5. Results default to 10 per page — check `has_more` and use `offset`.\n";
 
+/* ── OpenCode plugin (TypeScript, auto-discovered from ~/.config/opencode/plugins/) ──
+ * Installs a .ts plugin that wires tool.execute.after (grep/glob graph augment)
+ * and experimental.chat.system.transform (session reminder). The binary path is
+ * embedded at install time via fprintf %s — same pattern as the Claude Code
+ * hook gate script. Uses tool.execute.after (NOT .before) because .before output
+ * mutation has no effect on the tool result the model sees (verified against
+ * anomalyco/opencode source: packages/opencode/src/session/tools.ts). */
+static const char opencode_plugin_content[] =
+    "import type { Plugin } from \"@opencode-ai/plugin\"\n"
+    "import { spawn } from \"child_process\"\n"
+    "\n"
+    "const BIN = \"%s\"\n"
+    "\n"
+    "export default (async () => {\n"
+    "  return {\n"
+    "    \"tool.execute.after\": async (input: { tool: string; args: any }, "
+    "output: { output: string }) => {\n"
+    "      if (input.tool !== \"grep\" && input.tool !== \"glob\") return\n"
+    "      const pattern = input.args?.pattern\n"
+    "      if (!pattern) return\n"
+    "      const toolName = input.tool === \"grep\" ? \"Grep\" : \"Glob\"\n"
+    "      try {\n"
+    "        const payload = JSON.stringify({ tool_name: toolName, "
+    "tool_input: { pattern } })\n"
+    "        const child = spawn(BIN, [\"hook-augment\"], "
+    "{ stdio: [\"pipe\", \"pipe\", \"ignore\"] })\n"
+    "        child.stdin.write(payload)\n"
+    "        child.stdin.end()\n"
+    "        let stdout = \"\"\n"
+    "        child.stdout.on(\"data\", (d: Buffer) => { stdout += d.toString() })\n"
+    "        await new Promise<void>((resolve) => {\n"
+    "          child.on(\"close\", () => resolve())\n"
+    "          child.on(\"error\", () => resolve())\n"
+    "        })\n"
+    "        if (!stdout.trim()) return\n"
+    "        const parsed = JSON.parse(stdout)\n"
+    "        const ctx = parsed?.hookSpecificOutput?.additionalContext\n"
+    "        if (typeof ctx === \"string\" && ctx.length > 0) {\n"
+    "          output.output += \"\\n\\n\" + ctx\n"
+    "        }\n"
+    "      } catch (e) {}\n"
+    "    },\n"
+    "    \"experimental.chat.system.transform\": async (_input: any, "
+    "output: { system: string[] }) => {\n"
+    "      output.system.push(\"Code discovery: prefer codebase-memory-mcp "
+    "(search_graph, trace_path, get_code_snippet, query_graph, search_code) "
+    "over grep/file-read; run index_repository first if the project is not "
+    "indexed.\")\n"
+    "    }\n"
+    "  }\n"
+    "}) satisfies Plugin\n";
+
 static const char codex_instructions_content[] =
     "# Codebase Knowledge Graph\n"
     "\n"
@@ -1668,6 +1720,67 @@ int cbm_remove_opencode_mcp(const char *config_path) {
     return rc;
 }
 
+/* ── OpenCode plugin install/remove ──────────────────────────────
+ * Writes the TypeScript plugin to ~/.config/opencode/plugins/cbm-augment.ts.
+ * OpenCode auto-discovers .ts files in this directory — no opencode.json entry
+ * needed. The plugin wires tool.execute.after (grep/glob graph augment) and
+ * experimental.chat.system.transform (session reminder). Follows the same
+ * TOCTOU-safe pattern as cbm_install_hook_gate_script: fchmod before fclose. */
+
+#define CMM_OPENCODE_PLUGIN_NAME "cbm-augment.ts"
+
+int cbm_upsert_opencode_plugin(const char *home, const char *binary_path, bool dry_run) {
+    if (!home || !binary_path) {
+        return CLI_ERR;
+    }
+    if (strchr(binary_path, '"') != NULL) {
+        return CLI_ERR;
+    }
+    char plugins_dir[CLI_BUF_1K];
+    snprintf(plugins_dir, sizeof(plugins_dir), "%s/.config/opencode/plugins", home);
+    if (!dry_run) {
+        cbm_mkdir_p(plugins_dir, CLI_OCTAL_PERM);
+    }
+
+    char plugin_path[CLI_BUF_1K];
+    snprintf(plugin_path, sizeof(plugin_path), "%s/%s", plugins_dir, CMM_OPENCODE_PLUGIN_NAME);
+
+    if (dry_run) {
+        return 0;
+    }
+
+    FILE *f = fopen(plugin_path, "w");
+    if (!f) {
+        return CLI_ERR;
+    }
+    (void)fprintf(f, opencode_plugin_content, binary_path);
+#ifndef _WIN32
+    fchmod(fileno(f), CLI_OCTAL_PERM);
+#endif
+    (void)fclose(f);
+#ifdef _WIN32
+    chmod(plugin_path, CLI_OCTAL_PERM);
+#endif
+    return 0;
+}
+
+int cbm_remove_opencode_plugin(const char *home, bool dry_run) {
+    if (!home) {
+        return CLI_ERR;
+    }
+    char plugin_path[CLI_BUF_1K];
+    snprintf(plugin_path, sizeof(plugin_path), "%s/.config/opencode/plugins/%s",
+             home, CMM_OPENCODE_PLUGIN_NAME);
+    if (dry_run) {
+        return 0;
+    }
+    struct stat st;
+    if (stat(plugin_path, &st) == 0) {
+        return cbm_unlink(plugin_path);
+    }
+    return 0;
+}
+
 /* ── Antigravity MCP config (JSON, same mcpServers format) ────── */
 
 int cbm_upsert_antigravity_mcp(const char *binary_path, const char *config_path) {
@@ -3135,10 +3248,36 @@ static void install_cli_agent_configs(const cbm_detected_agents_t *agents, const
     if (agents->opencode) {
         char cp[CLI_BUF_1K];
         char ip[CLI_BUF_1K];
+        char skills_dir[CLI_BUF_1K];
         snprintf(cp, sizeof(cp), "%s/.config/opencode/opencode.json", home);
         snprintf(ip, sizeof(ip), "%s/.config/opencode/AGENTS.md", home);
+        snprintf(skills_dir, sizeof(skills_dir), "%s/.config/opencode/skills", home);
+
+        /* Plan mode: record planned writes for skills + plugin, mutate nothing
+         * (#388). MCP config + instructions are recorded by install_generic_agent_config. */
+        if (g_install_plan) {
+            char plugin_path[CLI_BUF_1K];
+            snprintf(plugin_path, sizeof(plugin_path),
+                     "%s/.config/opencode/plugins/%s", home, CMM_OPENCODE_PLUGIN_NAME);
+            plan_record("OpenCode", "skills", skills_dir);
+            plan_record("OpenCode", "plugin", plugin_path);
+        }
+
         install_generic_agent_config("OpenCode", binary_path, cp, ip, dry_run,
                                      cbm_upsert_opencode_mcp);
+
+        if (!g_install_plan) {
+            /* Install skills (same consolidated skill as Claude Code). */
+            int skill_count = cbm_install_skills(skills_dir, true, dry_run);
+            printf("  skills: %d installed\n", skill_count);
+
+            /* Install TypeScript plugin (tool.execute.after + system.transform). */
+            if (!dry_run) {
+                cbm_upsert_opencode_plugin(home, binary_path, dry_run);
+            }
+            printf("  plugin: tool.execute.after (Grep/Glob graph augment) + "
+                   "experimental.chat.system.transform (session reminder)\n");
+        }
     }
     if (agents->antigravity) {
         char cp[CLI_BUF_1K];
@@ -3632,10 +3771,20 @@ static void uninstall_cli_agents(const cbm_detected_agents_t *agents, const char
     if (agents->opencode) {
         char cp[CLI_BUF_1K];
         char ip[CLI_BUF_1K];
+        char skills_dir[CLI_BUF_1K];
         snprintf(cp, sizeof(cp), "%s/.config/opencode/opencode.json", home);
         snprintf(ip, sizeof(ip), "%s/.config/opencode/AGENTS.md", home);
+        snprintf(skills_dir, sizeof(skills_dir), "%s/.config/opencode/skills", home);
         uninstall_agent_mcp_instr((mcp_uninstall_args_t){"OpenCode", cp, ip}, dry_run,
                                   cbm_remove_opencode_mcp);
+        /* Remove skills. */
+        int removed = cbm_remove_skills(skills_dir, dry_run);
+        printf("OpenCode: removed %d skill(s)\n", removed);
+        /* Remove TypeScript plugin. */
+        if (!dry_run) {
+            cbm_remove_opencode_plugin(home, dry_run);
+        }
+        printf("  removed plugin\n");
     }
     if (agents->antigravity) {
         char cp[CLI_BUF_1K];
 
@@ -148,6 +148,15 @@ int cbm_upsert_opencode_mcp(const char *binary_path, const char *config_path);
 /* Remove CMM MCP entry from opencode.json. Returns 0 on success. */
 int cbm_remove_opencode_mcp(const char *config_path);
 
+/* OpenCode: install TypeScript plugin to ~/.config/opencode/plugins/cbm-augment.ts.
+ * Wires tool.execute.after (grep/glob graph augment) and
+ * experimental.chat.system.transform (session reminder).
+ * Returns 0 on success. */
+int cbm_upsert_opencode_plugin(const char *home, const char *binary_path, bool dry_run);
+
+/* Remove the OpenCode plugin file. Returns 0 on success. */
+int cbm_remove_opencode_plugin(const char *home, bool dry_run);
+
 /* Antigravity: upsert MCP entry in ~/.gemini/antigravity/mcp_config.json.
  * Returns 0 on success. */
 int cbm_upsert_antigravity_mcp(const char *binary_path, const char *config_path);
 
@@ -1963,6 +1963,129 @@ TEST(cli_upsert_opencode_mcp_existing) {
     PASS();
 }
 
+/* ═══════════════════════════════════════════════════════════════════
+ *  Group B: OpenCode Plugin + Skills
+ * ═══════════════════════════════════════════════════════════════════ */
+
+TEST(cli_upsert_opencode_plugin_fresh) {
+    char tmpdir[256];
+    snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-ocode-plug-XXXXXX");
+    if (!cbm_mkdtemp(tmpdir))
+        FAIL("cbm_mkdtemp failed");
+
+    int rc = cbm_upsert_opencode_plugin(tmpdir, "/usr/local/bin/codebase-memory-mcp", false);
+    ASSERT_EQ(rc, 0);
+
+    char plugin_path[512];
+    snprintf(plugin_path, sizeof(plugin_path), "%s/.config/opencode/plugins/cbm-augment.ts",
+             tmpdir);
+    const char *data = read_test_file(plugin_path);
+    ASSERT_NOT_NULL(data);
+    ASSERT(strstr(data, "/usr/local/bin/codebase-memory-mcp") != NULL);
+    ASSERT(strstr(data, "tool.execute.after") != NULL);
+    ASSERT(strstr(data, "experimental.chat.system.transform") != NULL);
+    ASSERT(strstr(data, "hook-augment") != NULL);
+    ASSERT(strstr(data, "satisfies Plugin") != NULL);
+
+    test_rmdir_r(tmpdir);
+    PASS();
+}
+
+TEST(cli_upsert_opencode_plugin_idempotent) {
+    char tmpdir[256];
+    snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-ocode-plug2-XXXXXX");
+    if (!cbm_mkdtemp(tmpdir))
+        FAIL("cbm_mkdtemp failed");
+
+    /* First install */
+    int rc = cbm_upsert_opencode_plugin(tmpdir, "/usr/local/bin/codebase-memory-mcp", false);
+    ASSERT_EQ(rc, 0);
+
+    /* Re-install with different path — should overwrite cleanly */
+    rc = cbm_upsert_opencode_plugin(tmpdir, "/opt/cbm/codebase-memory-mcp", false);
+    ASSERT_EQ(rc, 0);
+
+    char plugin_path[512];
+    snprintf(plugin_path, sizeof(plugin_path), "%s/.config/opencode/plugins/cbm-augment.ts",
+             tmpdir);
+    const char *data = read_test_file(plugin_path);
+    ASSERT_NOT_NULL(data);
+    ASSERT(strstr(data, "/opt/cbm/codebase-memory-mcp") != NULL);
+    ASSERT(strstr(data, "/usr/local/bin/codebase-memory-mcp") == NULL);
+
+    test_rmdir_r(tmpdir);
+    PASS();
+}
+
+TEST(cli_upsert_opencode_plugin_rejects_quote) {
+    char tmpdir[256];
+    snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-ocode-plug3-XXXXXX");
+    if (!cbm_mkdtemp(tmpdir))
+        FAIL("cbm_mkdtemp failed");
+
+    /* Binary path containing a double-quote must be rejected (security). */
+    int rc = cbm_upsert_opencode_plugin(tmpdir, "/usr/local/bin/\"evil\"", false);
+    ASSERT_NEQ(rc, 0);
+
+    test_rmdir_r(tmpdir);
+    PASS();
+}
+
+TEST(cli_remove_opencode_plugin) {
+    char tmpdir[256];
+    snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-ocode-plug4-XXXXXX");
+    if (!cbm_mkdtemp(tmpdir))
+        FAIL("cbm_mkdtemp failed");
+
+    /* Install then remove */
+    int rc = cbm_upsert_opencode_plugin(tmpdir, "/usr/local/bin/codebase-memory-mcp", false);
+    ASSERT_EQ(rc, 0);
+
+    char plugin_path[512];
+    snprintf(plugin_path, sizeof(plugin_path), "%s/.config/opencode/plugins/cbm-augment.ts",
+             tmpdir);
+    struct stat st;
+    ASSERT(stat(plugin_path, &st) == 0);
+
+    rc = cbm_remove_opencode_plugin(tmpdir, false);
+    ASSERT_EQ(rc, 0);
+    ASSERT(stat(plugin_path, &st) != 0);
+
+    /* Remove again — should succeed (idempotent) */
+    rc = cbm_remove_opencode_plugin(tmpdir, false);
+    ASSERT_EQ(rc, 0);
+
+    test_rmdir_r(tmpdir);
+    PASS();
+}
+
+TEST(cli_opencode_skills_installed) {
+    char tmpdir[256];
+    snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-ocode-skill-XXXXXX");
+    if (!cbm_mkdtemp(tmpdir))
+        FAIL("cbm_mkdtemp failed");
+
+    char skills_dir[512];
+    snprintf(skills_dir, sizeof(skills_dir), "%s/skills", tmpdir);
+
+    int count = cbm_install_skills(skills_dir, true, false);
+    ASSERT_EQ(count, CBM_SKILL_COUNT);
+
+    char skill_file[512];
+    snprintf(skill_file, sizeof(skill_file), "%s/codebase-memory/SKILL.md", skills_dir);
+    const char *data = read_test_file(skill_file);
+    ASSERT_NOT_NULL(data);
+    ASSERT(strstr(data, "codebase-memory") != NULL);
+    ASSERT(strstr(data, "search_graph") != NULL);
+
+    /* Remove skills */
+    int removed = cbm_remove_skills(skills_dir, false);
+    ASSERT_EQ(removed, CBM_SKILL_COUNT);
+
+    test_rmdir_r(tmpdir);
+    PASS();
+}
+
 /* ═══════════════════════════════════════════════════════════════════
  *  Group B: MCP Config Upsert — Antigravity
  * ═══════════════════════════════════════════════════════════════════ */
@@ -2770,6 +2893,13 @@ SUITE(cli) {
     RUN_TEST(cli_upsert_opencode_mcp_fresh);
     RUN_TEST(cli_upsert_opencode_mcp_existing);
 
+    /* OpenCode plugin + skills (5 tests — group B) */
+    RUN_TEST(cli_upsert_opencode_plugin_fresh);
+    RUN_TEST(cli_upsert_opencode_plugin_idempotent);
+    RUN_TEST(cli_upsert_opencode_plugin_rejects_quote);
+    RUN_TEST(cli_remove_opencode_plugin);
+    RUN_TEST(cli_opencode_skills_installed);
+
     /* Antigravity MCP config upsert (2 tests — group B) */
     RUN_TEST(cli_upsert_antigravity_mcp_fresh);
     RUN_TEST(cli_upsert_antigravity_mcp_replace);