feat(agents): wire agent_definitions and opencode.json agents into precedence chain

- Modified agent-config-handler.ts to load and integrate both new agent sources
- Added loadAgentDefinitions() and readOpencodeConfigAgents() calls in loading phase
- Integrated both sources into agent precedence chains (both Sisyphus-enabled and disabled paths)
- Added detailed logging for new agent sources
- Added filtering logic to respect disabled_agents configuration
- Extended agent-config-handler.test.ts with 7 new integration tests
- All tests passing (18/18 integration, 65/65 loader suite)

Wave 3 of agent definitions enhancement complete.

src/features/claude-code-agent-loader/index.ts

@@ -1,2 +1,5 @@
 export * from "./types"
 export * from "./loader"
+export * from "./agent-definitions-loader"
+export * from "./opencode-config-agents-reader"
+export * from "./json-agent-loader"

src/features/claude-code-agent-loader/opencode-config-agents-reader.test.ts

@@ -229,6 +229,34 @@ describe("readOpencodeConfigAgents", () => {
     fs.rmSync(tempDir, { recursive: true })
   })
 
+  it("supports agent key as fallback when agents key is not present", () => {
+    const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "opencode-test-"))
+    const opencodeDir = path.join(tempDir, ".opencode")
+    fs.mkdirSync(opencodeDir, { recursive: true })
+
+    const configPath = path.join(opencodeDir, "opencode.json")
+    fs.writeFileSync(
+      configPath,
+      JSON.stringify({
+        agent: {
+          "fallback-agent": {
+            description: "Using agent key",
+            mode: "subagent",
+            prompt: "Fallback prompt",
+          },
+        },
+      })
+    )
+
+    const result = readOpencodeConfigAgents(tempDir)
+
+    expect(result).toHaveProperty("fallback-agent")
+    expect(result["fallback-agent"].description).toBe("(opencode-config) Using agent key")
+    expect(result["fallback-agent"].prompt).toBe("Fallback prompt")
+
+    fs.rmSync(tempDir, { recursive: true })
+  })
+
   it("prioritizes project-level opencode.json over user-level", () => {
     const projectDir = fs.mkdtempSync(path.join(os.tmpdir(), "opencode-project-"))
     const projectOpencodeDir = path.join(projectDir, ".opencode")

src/features/claude-code-agent-loader/opencode-config-agents-reader.ts

@@ -9,6 +9,7 @@ import type { ClaudeCodeAgentConfig } from "./types"
 
 interface OpencodeConfigWithAgents {
   agents?: Record<string, unknown>
+  agent?: Record<string, unknown>
   agent_definitions?: string | string[]
 }
 
@@ -103,8 +104,10 @@ export function readOpencodeConfigAgents(directory: string): Record<string, Clau
 
       const configDir = path.dirname(configPath)
 
-      if (parseResult.data.agents && typeof parseResult.data.agents === "object") {
-        for (const [agentName, agentData] of Object.entries(parseResult.data.agents)) {
+      const agentsToLoad = parseResult.data.agents || parseResult.data.agent
+
+      if (agentsToLoad && typeof agentsToLoad === "object") {
+        for (const [agentName, agentData] of Object.entries(agentsToLoad)) {
           const converted = convertInlineAgent(agentData)
           if (converted) {
             result[agentName] = converted