feat(shared): add replaceToolArgs helper for safe tool-args mutation

opencode >=1.14 freezes output.args via Immer before plugin hooks run.
Direct property assignment or Object.assign on a frozen object throws
TypeError. This helper replaces output.args with a shallow clone
containing the patch, avoiding mutation of the frozen original.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/index.ts

@@ -84,3 +84,4 @@ export * from "./task-system-enabled"
 export * from "./parse-tools-config"
 export { parseModelString } from "./model-string-parser"
 export { EXCLUDED_DIRS } from "./excluded-dirs"
+export * from "./replace-tool-args"

src/shared/replace-tool-args.ts

@@ -0,0 +1,16 @@
+/**
+ * Safely replace tool arguments without mutating frozen objects.
+ *
+ * opencode >=1.14 may freeze `output.args` via Immer before plugin hooks run.
+ * Direct property assignment (`output.args.key = value`) or `Object.assign(output.args, patch)`
+ * throws `TypeError: Attempted to assign to readonly property` on a frozen object.
+ *
+ * This helper replaces `output.args` with a shallow clone containing the patch,
+ * which works regardless of whether the original args object is frozen.
+ */
+export function replaceToolArgs(
+	output: { args: Record<string, unknown> },
+	patch: Record<string, unknown>,
+): void {
+	output.args = { ...output.args, ...patch }
+}