fix(source-control): reach users Orca already pinned to Pi's Copilot default

Orca seeded selectedModelByAgent.pi = github-copilot/gpt-5.4-mini the first
time a user picked Pi on a pre-fix build, and pi --list-models still lists
that id, so the resolution chain honoured it and STA-4249 kept reproducing
for every upgrading user. Every prior test started from an empty selection.

src/shared/commit-message-agent-spec.ts

@@ -109,6 +109,14 @@ const CLAUDE_THINKING_LEVELS: ThinkingLevel[] = [
 
 const PI_DEFAULT_MODEL_ID = 'default'
 
+/**
+ * The model id Orca used to persist for Pi before `Pi default` existed. Orca itself
+ * seeded this into `selectedModelByAgent.pi` the first time a user picked Pi, so a
+ * pre-upgrade user carries it even though they never chose a Copilot model. Treated
+ * as "no selection" on read so the fix reaches them (STA-4249).
+ */
+export const PI_RETIRED_COPILOT_DEFAULT_MODEL_ID = 'github-copilot/gpt-5.4-mini'
+
 function uniqueModels(models: CommitMessageModel[]): CommitMessageModel[] {
   const seen = new Set<string>()
   return models.filter((model) => {

src/shared/source-control-ai.test.ts

@@ -118,6 +118,38 @@ describe('source-control AI resolution', () => {
     }
   )
 
+  // Why: Orca seeded `github-copilot/gpt-5.4-mini` into selectedModelByAgent.pi the
+  // first time a user picked Pi on a pre-fix build, and `pi --list-models` still
+  // lists it, so the resolution chain honoured it and STA-4249 kept reproducing for
+  // every upgrading user. The other cases here all start from an empty selection.
+  it.each(['commitMessage', 'pullRequest', 'branchName'] as const)(
+    'ignores the retired Copilot default that Orca persisted for Pi, for %s',
+    (operation) => {
+      const base = piSettings()
+      base.sourceControlAi!.selectedModelByAgent = { pi: 'github-copilot/gpt-5.4-mini' }
+      base.commitMessageAi!.selectedModelByAgent = { pi: 'github-copilot/gpt-5.4-mini' }
+      base.sourceControlAi!.discoveredModelsByAgent = {
+        pi: [{ id: 'github-copilot/gpt-5.4-mini', label: 'GPT-5.4 mini' }]
+      }
+
+      const resolved = resolveSourceControlAiForOperation({
+        settings: base,
+        repo: null,
+        operation,
+        discoveryHostKey: 'local'
+      })
+      expect(resolved.ok).toBe(true)
+      if (!resolved.ok) {
+        throw new Error(resolved.error)
+      }
+      const result = planCommitMessageGeneration(resolved.value.params, 'PROMPT')
+
+      expect(result).toMatchObject({ ok: true })
+      expect(result.ok && result.plan.args).not.toContain('--model')
+      expect(result.ok && result.plan.args).not.toContain('github-copilot/gpt-5.4-mini')
+    }
+  )
+
   it.each(['commitMessage', 'pullRequest', 'branchName'] as const)(
     'passes an explicit Pi model override for %s',
     (operation) => {

src/shared/source-control-ai.ts

@@ -8,7 +8,8 @@ import {
   listCommitMessageAgentCapabilities,
   type CustomAgentId,
   isCustomAgentId,
-  resolveCommitMessageAgentChoice
+  resolveCommitMessageAgentChoice,
+  PI_RETIRED_COPILOT_DEFAULT_MODEL_ID
 } from './commit-message-agent-spec'
 import { LOCAL_COMMIT_MESSAGE_HOST_KEY } from './commit-message-host-key'
 import {
@@ -949,7 +950,7 @@ function selectPersistedModelId(args: {
   defaultModelId: string
 }): string {
   const { source, legacy, repoOverrides, operation, hostKey, agentId, defaultModelId } = args
-  return (
+  const persisted =
     readSourceControlAiModelChoiceForHost(
       repoOverrides?.modelOverridesByOperation?.[operation],
       hostKey,
@@ -966,7 +967,14 @@ function selectPersistedModelId(args: {
       ? legacy?.selectedModelByAgent?.[agentId]
       : undefined) ??
     defaultModelId
-  )
+  // Why: Orca seeded `github-copilot/gpt-5.4-mini` into Pi's persisted selection
+  // before `Pi default` existed, so a pre-upgrade user is pinned to a Copilot model
+  // they never chose and STA-4249 would still reproduce for them. Discovery still
+  // lists that id, so the resolution chain below would otherwise honour it.
+  if (agentId === 'pi' && persisted === PI_RETIRED_COPILOT_DEFAULT_MODEL_ID) {
+    return defaultModelId
+  }
+  return persisted
 }
 
 function resolveThinkingLevel(args: {