Honor workflow-level COPILOT_MODEL in Copilot BYOK smoke workflows (#4876)

* Initial plan

* fix: honor workflow COPILOT_MODEL in BYOK smoke

* docs: clarify BYOK model rewrite comment

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

.github/workflows/smoke-copilot-byok-aoai-apikey.lock.yml

@@ -291,8 +291,8 @@ const legacyApiProxyLogsDirRegex =
 const copySessionStateStepRegex =
   /^(\s+)- name: Copy Copilot session state files to logs\n\1  if: always\(\)\n\1  continue-on-error: true\n\1  run: bash "\$\{RUNNER_TEMP\}\/gh-aw\/actions\/copy_copilot_session_state\.sh"\n/m;
 
-const copilotModelEmptyFallbackRegex =
-  /(COPILOT_MODEL:\s*\$\{\{\s*vars\.GH_AW_MODEL_AGENT_COPILOT\s*\|\|\s*)(?:vars\.GH_AW_DEFAULT_MODEL_COPILOT\s*\|\|\s*)?'[^']*'(\s*\}\})/g;
+const copilotModelOverrideRegex =
+  /^(\s*COPILOT_MODEL:\s*)\$\{\{\s*(?:vars\.GH_AW_MODEL_AGENT_COPILOT\s*\|\|\s*)?(?:vars\.GH_AW_DEFAULT_MODEL_COPILOT\s*\|\|\s*)?(?:env\.COPILOT_MODEL|''|'[^']*')\s*\}\}[ \t]*$/gm;
 
 function buildCopySessionStateStep(indent: string): string {
   const i = indent;
@@ -429,52 +429,61 @@ describe('buildCopySessionStateStep', () => {
   });
 });
 
-describe('copilotModelEmptyFallbackRegex', () => {
+describe('copilotModelOverrideRegex', () => {
   beforeEach(() => {
-    copilotModelEmptyFallbackRegex.lastIndex = 0;
+    copilotModelOverrideRegex.lastIndex = 0;
   });
 
-  it('should replace empty fallback with env.COPILOT_MODEL', () => {
+  it('should replace empty fallback with workflow-level env.COPILOT_MODEL', () => {
     const input = "          COPILOT_MODEL: ${{ vars.GH_AW_MODEL_AGENT_COPILOT || '' }}\n";
     const result = input.replace(
-      copilotModelEmptyFallbackRegex,
-      `$1env.COPILOT_MODEL$2`
+      copilotModelOverrideRegex,
+      '$1${{ env.COPILOT_MODEL }}'
     );
     expect(result).toBe(
-      `          COPILOT_MODEL: \${{ vars.GH_AW_MODEL_AGENT_COPILOT || env.COPILOT_MODEL }}\n`
+      `          COPILOT_MODEL: \${{ env.COPILOT_MODEL }}\n`
     );
   });
 
-  it('should replace hardcoded model fallback with env.COPILOT_MODEL', () => {
+  it('should replace hardcoded model fallback with workflow-level env.COPILOT_MODEL', () => {
     const input =
       "          COPILOT_MODEL: ${{ vars.GH_AW_MODEL_AGENT_COPILOT || 'claude-opus-4.8' }}\n";
     const result = input.replace(
-      copilotModelEmptyFallbackRegex,
-      `$1env.COPILOT_MODEL$2`
+      copilotModelOverrideRegex,
+      '$1${{ env.COPILOT_MODEL }}'
     );
     expect(result).toBe(
-      `          COPILOT_MODEL: \${{ vars.GH_AW_MODEL_AGENT_COPILOT || env.COPILOT_MODEL }}\n`
+      `          COPILOT_MODEL: \${{ env.COPILOT_MODEL }}\n`
     );
   });
 
   it('should replace fallback chain with vars.GH_AW_DEFAULT_MODEL_COPILOT link', () => {
     const input =
       "          COPILOT_MODEL: ${{ vars.GH_AW_MODEL_AGENT_COPILOT || vars.GH_AW_DEFAULT_MODEL_COPILOT || 'claude-sonnet-4.6' }}\n";
     const result = input.replace(
-      copilotModelEmptyFallbackRegex,
-      `$1env.COPILOT_MODEL$2`
+      copilotModelOverrideRegex,
+      '$1${{ env.COPILOT_MODEL }}'
     );
     expect(result).toBe(
-      `          COPILOT_MODEL: \${{ vars.GH_AW_MODEL_AGENT_COPILOT || env.COPILOT_MODEL }}\n`
+      `          COPILOT_MODEL: \${{ env.COPILOT_MODEL }}\n`
     );
   });
 
-  it('should not modify already-rewritten env.COPILOT_MODEL fallback', () => {
+  it('should replace repo-level override fallback with workflow-level env.COPILOT_MODEL', () => {
     const input =
       "          COPILOT_MODEL: ${{ vars.GH_AW_MODEL_AGENT_COPILOT || env.COPILOT_MODEL }}\n";
     const result = input.replace(
-      copilotModelEmptyFallbackRegex,
-      `$1env.COPILOT_MODEL$2`
+      copilotModelOverrideRegex,
+      '$1${{ env.COPILOT_MODEL }}'
+    );
+    expect(result).toBe(`          COPILOT_MODEL: \${{ env.COPILOT_MODEL }}\n`);
+  });
+
+  it('should be idempotent when already using workflow-level env.COPILOT_MODEL', () => {
+    const input = "          COPILOT_MODEL: ${{ env.COPILOT_MODEL }}\n";
+    const result = input.replace(
+      copilotModelOverrideRegex,
+      '$1${{ env.COPILOT_MODEL }}'
     );
     expect(result).toBe(input);
   });

.github/workflows/smoke-copilot-byok-aoai-entra.lock.yml

@@ -110,18 +110,15 @@ const legacyApiProxyLogsDirRegex =
 // postinstall script downloads the platform-specific native binary.  Without it,
 // `claude` fails with "native binary not installed".
 
-// Work around gh-aw compiler bug (gh-aw#26565) where Copilot model fallback is
-// emitted at the step level and overrides the workflow-level COPILOT_MODEL env
-// when the repo variables are unset. Older compilers emitted an empty string
-// fallback (`|| ''`); newer compilers emit a hardcoded default model
-// (`|| 'claude-sonnet-4.6'`) and may add an extra `vars.GH_AW_DEFAULT_MODEL_COPILOT`
-// link in the fallback chain. In both cases the step-level value wins over the
-// workflow-level `env: COPILOT_MODEL: ...` we set on BYOK smoke workflows, which
-// breaks targeted BYOK testing (e.g. forcing `o4-mini-aw` against Azure OpenAI).
-// We replace the entire expression with `env.COPILOT_MODEL` so the step inherits
-// the workflow-level default verbatim.
-const copilotModelEmptyFallbackRegex =
-  /(COPILOT_MODEL:\s*\$\{\{\s*vars\.GH_AW_MODEL_AGENT_COPILOT\s*\|\|\s*)(?:vars\.GH_AW_DEFAULT_MODEL_COPILOT\s*\|\|\s*)?'[^']*'(\s*\}\})/g;
+// Work around gh-aw compiler bug (gh-aw#26565) where Copilot model selection is
+// emitted at the step level for BYOK smoke workflows, overriding the
+// workflow-level `env: COPILOT_MODEL: ...` that intentionally pins a
+// low-cost/provider-specific model (for example `claude-haiku-4.5` or
+// `o4-mini-aw`). Normalize every compiled step-level COPILOT_MODEL expression
+// back to `${{ env.COPILOT_MODEL }}` so the workflow-level setting wins even if
+// repo-level default model variables are configured.
+const copilotModelOverrideRegex =
+  /^(\s*COPILOT_MODEL:\s*)\$\{\{\s*(?:vars\.GH_AW_MODEL_AGENT_COPILOT\s*\|\|\s*)?(?:vars\.GH_AW_DEFAULT_MODEL_COPILOT\s*\|\|\s*)?(?:env\.COPILOT_MODEL|''|'[^']*')\s*\}\}[ \t]*$/gm;
 
 // Sentinel used to detect whether the "Copy Copilot session state" step has
 // already been replaced with the AWF-aware inline script.
@@ -542,20 +539,21 @@ for (const workflowPath of workflowPaths) {
     }
   }
 
-  // For smoke-copilot-byok variants: replace empty model fallbacks with the
-  // workflow-level COPILOT_MODEL env so the generated step inherits the shared
-  // default without hardcoding a duplicate model string here.
+  // For smoke-copilot-byok variants: replace compiled COPILOT_MODEL override
+  // expressions with the workflow-level COPILOT_MODEL env so the generated
+  // step inherits the intended BYOK model instead of any repo-level default.
   const isCopilotByokSmoke = /smoke-copilot-byok[^/]*\.lock\.yml$/.test(workflowPath);
   if (isCopilotByokSmoke) {
-    const emptyFallbackMatches = content.match(copilotModelEmptyFallbackRegex);
-    if (emptyFallbackMatches) {
-      content = content.replace(
-        copilotModelEmptyFallbackRegex,
-        '$1env.COPILOT_MODEL$2'
-      );
+    const rewrittenContent = content.replace(
+      copilotModelOverrideRegex,
+      '$1${{ env.COPILOT_MODEL }}'
+    );
+    if (rewrittenContent !== content) {
+      const rewrittenCount = (content.match(copilotModelOverrideRegex) || []).length;
+      content = rewrittenContent;
       modified = true;
       console.log(
-        `  Replaced ${emptyFallbackMatches.length} empty COPILOT_MODEL fallback(s) for BYOK smoke`
+        `  Rewrote ${rewrittenCount} COPILOT_MODEL override(s) to env.COPILOT_MODEL for BYOK smoke`
       );
     }
   }

.github/workflows/smoke-copilot-byok.lock.yml

@@ -0,0 +1,26 @@
+import * as fs from 'fs';
+import * as path from 'path';
+
+const workflowsDir = path.resolve(__dirname, '../../.github/workflows');
+
+const byokSourcePath = path.join(workflowsDir, 'smoke-copilot-byok.md');
+const byokLockPaths = [
+  path.join(workflowsDir, 'smoke-copilot-byok.lock.yml'),
+  path.join(workflowsDir, 'smoke-copilot-byok-aoai-apikey.lock.yml'),
+  path.join(workflowsDir, 'smoke-copilot-byok-aoai-entra.lock.yml'),
+];
+
+describe('smoke copilot BYOK workflow model selection', () => {
+  it('pins the direct BYOK source workflow to claude-haiku-4.5', () => {
+    const source = fs.readFileSync(byokSourcePath, 'utf-8');
+
+    expect(source).toContain('COPILOT_MODEL: claude-haiku-4.5');
+  });
+
+  it.each(byokLockPaths)('forces workflow-level COPILOT_MODEL in %s', (lockPath) => {
+    const lock = fs.readFileSync(lockPath, 'utf-8');
+
+    expect(lock).toContain('COPILOT_MODEL: ${{ env.COPILOT_MODEL }}');
+    expect(lock).not.toContain('COPILOT_MODEL: ${{ vars.GH_AW_MODEL_AGENT_COPILOT || env.COPILOT_MODEL }}');
+  });
+});