fix: preserve AGENTS.md in context

lib/request/request-transformer.ts

@@ -324,11 +324,58 @@ export function isOpenCodeSystemPrompt(
 	return contentText.startsWith("You are a coding agent running in");
 }
 
+/**
+ * Extract content text from an input item
+ * @param item - Input item
+ * @returns Content as string
+ */
+function getContentText(item: InputItem): string {
+	if (typeof item.content === "string") {
+		return item.content;
+	}
+	if (Array.isArray(item.content)) {
+		return item.content
+			.filter((c) => c.type === "input_text" && c.text)
+			.map((c) => c.text)
+			.join("\n");
+	}
+	return "";
+}
+
+/**
+ * Extract AGENTS.md content from a concatenated OpenCode message
+ *
+ * OpenCode concatenates multiple pieces into a single developer message:
+ * 1. Base codex.txt prompt (starts with "You are a coding agent running in...")
+ * 2. Environment info
+ * 3. <files> block
+ * 4. AGENTS.md content (prefixed with "Instructions from: /path/to/AGENTS.md")
+ *
+ * This function extracts the AGENTS.md portions so they can be preserved
+ * when filtering out the OpenCode base prompt.
+ *
+ * @param contentText - The full content text of the message
+ * @returns The AGENTS.md content if found, null otherwise
+ */
+function extractAgentsMdContent(contentText: string): string | null {
+	const marker = "Instructions from:";
+	const idx = contentText.indexOf(marker);
+	if (idx > 0) {
+		return contentText.slice(idx).trimStart();
+	}
+	return null;
+}
+
 /**
  * Filter out OpenCode system prompts from input
  * Used in CODEX_MODE to replace OpenCode prompts with Codex-OpenCode bridge
+ *
+ * When OpenCode sends a concatenated message containing both the base prompt
+ * AND AGENTS.md content, this function extracts and preserves the AGENTS.md
+ * portions while filtering out the OpenCode base prompt.
+ *
  * @param input - Input array
- * @returns Input array without OpenCode system prompts
+ * @returns Input array without OpenCode system prompts (but with AGENTS.md preserved)
  */
 export async function filterOpenCodeSystemPrompts(
 	input: InputItem[] | undefined,
@@ -344,12 +391,39 @@ export async function filterOpenCodeSystemPrompts(
 		// This is safe because we still have the "starts with" check
 	}
 
-	return input.filter((item) => {
-		// Keep user messages
-		if (item.role === "user") return true;
-		// Filter out OpenCode system prompts
-		return !isOpenCodeSystemPrompt(item, cachedPrompt);
-	});
+	const result: InputItem[] = [];
+
+	for (const item of input) {
+		// Keep user messages as-is
+		if (item.role === "user") {
+			result.push(item);
+			continue;
+		}
+
+		// Check if this is an OpenCode system prompt
+		if (isOpenCodeSystemPrompt(item, cachedPrompt)) {
+			// OpenCode may concatenate AGENTS.md content with the base prompt
+			// Extract and preserve any AGENTS.md content
+			const contentText = getContentText(item);
+			const agentsMdContent = extractAgentsMdContent(contentText);
+
+			if (agentsMdContent) {
+				// Create a new message with just the AGENTS.md content
+				result.push({
+					type: "message",
+					role: "developer",
+					content: agentsMdContent,
+				});
+			}
+			// Filter out the OpenCode base prompt (don't add original item)
+			continue;
+		}
+
+		// Keep all other messages
+		result.push(item);
+	}
+
+	return result;
 }
 
 /**

test/request-transformer.test.ts

@@ -544,6 +544,133 @@ describe('Request Transformer Module', () => {
 		it('should return undefined for undefined input', async () => {
 			expect(await filterOpenCodeSystemPrompts(undefined)).toBeUndefined();
 		});
+
+		// Tests for concatenated messages (single message containing both prompt AND AGENTS.md)
+		// This is how OpenCode actually sends content (as of v1.0.164+).
+		// The tests above cover separate messages pattern which may also occur.
+		describe('concatenated messages (OpenCode v1.0.164+ pattern)', () => {
+			it('should extract and preserve AGENTS.md when concatenated with OpenCode prompt', async () => {
+				// OpenCode sends a SINGLE message containing:
+				// 1. Base codex.txt prompt
+				// 2. Environment info
+				// 3. <files> block
+				// 4. AGENTS.md content (prefixed with "Instructions from:")
+				const input: InputItem[] = [
+					{
+						type: 'message',
+						role: 'developer',
+						content: `You are a coding agent running in the opencode, a terminal-based coding assistant.
+
+Here is some useful information about the environment you are running in:
+<env>
+  Working directory: /Users/test/project
+  Platform: darwin
+</env>
+<files>
+  src/
+    index.ts
+</files>
+Instructions from: /Users/test/project/AGENTS.md
+# Project Guidelines
+
+Use TypeScript for all new code.
+Follow existing patterns in the codebase.
+
+Instructions from: /Users/test/.config/opencode/AGENTS.md
+# Global Settings
+
+Always use mise for tool management.`,
+					},
+					{ type: 'message', role: 'user', content: 'hello' },
+				];
+
+				const result = await filterOpenCodeSystemPrompts(input);
+
+				// Should have 2 messages: extracted AGENTS.md content + user message
+				expect(result).toHaveLength(2);
+				expect(result![0].role).toBe('developer');
+				expect(result![0].content).toContain('Instructions from:');
+				expect(result![0].content).toContain('Project Guidelines');
+				expect(result![0].content).toContain('Global Settings');
+				// Should NOT contain the OpenCode base prompt
+				expect(result![0].content).not.toContain('You are a coding agent running in');
+				expect(result![1].role).toBe('user');
+			});
+
+			it('should preserve multiple AGENTS.md files in concatenated message', async () => {
+				const input: InputItem[] = [
+					{
+						type: 'message',
+						role: 'developer',
+						content: `You are a coding agent running in the opencode...
+
+Instructions from: /project/AGENTS.md
+# Project AGENTS.md
+Project-specific instructions here.
+
+Instructions from: /project/src/AGENTS.md
+# Nested AGENTS.md
+More specific instructions for src folder.
+
+Instructions from: ~/.config/opencode/AGENTS.md
+# Global AGENTS.md
+Global instructions here.`,
+					},
+					{ type: 'message', role: 'user', content: 'test' },
+				];
+
+				const result = await filterOpenCodeSystemPrompts(input);
+
+				expect(result).toHaveLength(2);
+				// All AGENTS.md content should be preserved
+				expect(result![0].content).toContain('Project AGENTS.md');
+				expect(result![0].content).toContain('Nested AGENTS.md');
+				expect(result![0].content).toContain('Global AGENTS.md');
+			});
+
+			it('should handle concatenated message with no AGENTS.md (just base prompt)', async () => {
+				const input: InputItem[] = [
+					{
+						type: 'message',
+						role: 'developer',
+						content: 'You are a coding agent running in the opencode, a terminal-based coding assistant.',
+					},
+					{ type: 'message', role: 'user', content: 'hello' },
+				];
+
+				const result = await filterOpenCodeSystemPrompts(input);
+
+				// Should just have the user message (base prompt filtered, no AGENTS.md to preserve)
+				expect(result).toHaveLength(1);
+				expect(result![0].role).toBe('user');
+			});
+
+			it('should handle array content format in concatenated message', async () => {
+				const input: InputItem[] = [
+					{
+						type: 'message',
+						role: 'developer',
+						content: [
+							{
+								type: 'input_text',
+								text: `You are a coding agent running in the opencode...
+
+Instructions from: /project/AGENTS.md
+# My Custom Instructions
+Do things this way.`,
+							},
+						],
+					},
+					{ type: 'message', role: 'user', content: 'hello' },
+				];
+
+				const result = await filterOpenCodeSystemPrompts(input);
+
+				expect(result).toHaveLength(2);
+				expect(result![0].content).toContain('My Custom Instructions');
+				expect(result![0].content).not.toContain('You are a coding agent');
+			});
+		});
 	});
 
 	describe('addCodexBridgeMessage', () => {