From 79ecea913d78ac92cb377f7f435585640562109b Mon Sep 17 00:00:00 2001
From: pi <pi@gitea.rwiesner.com>
Date: Sun, 12 Apr 2026 13:05:05 +0100
Subject: [PATCH] tool: avoid mutating discovered presets; use local normalized
 model values/shallow copies

---
 src/tool.ts | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/tool.ts b/src/tool.ts
index fd7bb05..f766652 100644
--- a/src/tool.ts
+++ b/src/tool.ts
@@ -104,6 +104,10 @@ export function createSubagentTool(deps: {
       const discovery = (deps.discoverSubagentPresets ?? discoverSubagentPresets)(ctx.cwd);
       const presets = discovery.presets;
 
+      // Note: presets are discovered/owned by the discovery layer and should be treated
+      // as immutable. Do not mutate preset objects in place. When a canonical/normalized
+      // model value is needed, use a local variable or a shallow copy of the preset.
+
       // Adapter: accept only the flattened shape { callModel?, presetModel? }
       // to keep the tool logic simple. If a resolver was injected with the
       // older test/hooks shape, we call it with both key names so it can read
@@ -207,7 +211,9 @@ export function createSubagentTool(deps: {
           params.model = normalized;
         }
 
-        // Validate preset default model if present
+        // Validate preset default model if present. Do not mutate discovered preset objects —
+        // keep a local normalized value (or a shallow copy when passing to runTask).
+        let normalizedPresetModelForSelection: string | undefined = undefined;
         if (preset.model !== undefined) {
           const normalizedPresetModel = normalizeModelReference(preset.model);
           if (!normalizedPresetModel) {
@@ -216,12 +222,11 @@ export function createSubagentTool(deps: {
               "single",
             );
           }
-          // Use canonical preset model
-          preset.model = normalizedPresetModel;
+          normalizedPresetModelForSelection = normalizedPresetModel;
         }
 
         // Ensure an effective model exists for this run (explicit override wins)
-        const singleSelection = callResolveChildModel({ callModel: params.model, presetModel: preset.model });
+        const singleSelection = callResolveChildModel({ callModel: params.model, presetModel: normalizedPresetModelForSelection });
         const singleRequested = singleSelection.requestedModel ?? params.model ?? preset.model;
         if (!singleRequested) {
           return makeErrorResult(
@@ -231,10 +236,11 @@ export function createSubagentTool(deps: {
         }
 
         try {
+          const presetForRun = normalizedPresetModelForSelection === undefined ? preset : { ...preset, model: normalizedPresetModelForSelection };
           const result = await runTask({
             task: params.task,
             cwd: params.cwd,
-            preset,
+            preset: presetForRun,
             taskModel: params.model,
             mode: "single",
           });
@@ -273,6 +279,8 @@ export function createSubagentTool(deps: {
           t.model = normalized;
         }
 
+        // Validate preset default model. Do not mutate the discovered preset object.
+        let normalizedPresetModelForTask: string | undefined = undefined;
         if (preset.model !== undefined) {
           const normalizedPresetModel = normalizeModelReference(preset.model);
           if (!normalizedPresetModel) {
@@ -281,12 +289,12 @@ export function createSubagentTool(deps: {
               "parallel",
             );
           }
-          preset.model = normalizedPresetModel;
+          normalizedPresetModelForTask = normalizedPresetModel;
         }
 
         // Ensure an effective model exists for this task
-        const sel = callResolveChildModel({ callModel: t.model, presetModel: preset.model });
-        const requested = sel.requestedModel ?? t.model ?? preset.model;
+        const sel = callResolveChildModel({ callModel: t.model, presetModel: normalizedPresetModelForTask });
+        const requested = sel.requestedModel ?? t.model ?? normalizedPresetModelForTask;
         if (!requested) {
           return makeErrorResult(
             `Parallel task ${index + 1} has no model. Provide an explicit 'model' or set a default model on preset "${preset.name}". Available models: ${availableModelsText}`,
@@ -311,12 +319,14 @@ export function createSubagentTool(deps: {
       const liveResults: SubagentRunResult[] = [];
       const results = await mapWithConcurrencyLimit(params.tasks, MAX_CONCURRENCY, async (task: any, index) => {
         const preset = presets.find((p) => p.name === task.preset)!;
+        const normalizedPresetModel = preset.model === undefined ? undefined : normalizeModelReference(preset.model);
+        const presetForRun = normalizedPresetModel === undefined ? preset : { ...preset, model: normalizedPresetModel };
         const result = await runTask({
           task: task.task,
           cwd: task.cwd,
           taskModel: task.model,
           taskIndex: index,
-          preset,
+          preset: presetForRun,
           mode: "parallel",
         });
         liveResults[index] = result;