fix(plugin): harden metadata recovery and extraction

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/atlas/subagent-session-id.test.ts

@@ -90,6 +90,17 @@ describe("extractSessionIdFromMetadata", () => {
     expect(result).toBe("ses_plugin_abc123")
   })
 
+  test("extracts legacy session aliases from tool metadata object", () => {
+    // given
+    const metadata = { sessionID: "ses_plugin_alias_123" }
+
+    // when
+    const result = extractSessionIdFromMetadata(metadata)
+
+    // then
+    expect(result).toBe("ses_plugin_alias_123")
+  })
+
   test("returns undefined for metadata without sessionId", () => {
     // given
     const metadata = { title: "some task" }

src/hooks/atlas/subagent-session-id.ts

@@ -1,30 +1,20 @@
 import type { PluginInput } from "@opencode-ai/plugin"
+import { extractTaskLink } from "../../features/tool-metadata-store"
 import { log } from "../../shared/logger"
 import { isSessionInBoulderLineage } from "./boulder-session-lineage"
 import { HOOK_NAME } from "./hook-name"
 
 export function extractSessionIdFromMetadata(metadata: unknown): string | undefined {
-  if (metadata && typeof metadata === "object" && "sessionId" in metadata) {
-    const value = (metadata as Record<string, unknown>).sessionId
-    if (typeof value === "string" && value.startsWith("ses_")) {
-      return value
-    }
+  const sessionId = extractTaskLink(metadata, "").sessionId
+  if (typeof sessionId === "string" && sessionId.startsWith("ses_")) {
+    return sessionId
   }
+
   return undefined
 }
 
 export function extractSessionIdFromOutput(output: string): string | undefined {
-  const taskMetadataBlocks = [...output.matchAll(/<task_metadata>([\s\S]*?)<\/task_metadata>/gi)]
-  const lastTaskMetadataBlock = taskMetadataBlocks.at(-1)?.[1]
-  if (lastTaskMetadataBlock) {
-    const taskMetadataSessionMatch = lastTaskMetadataBlock.match(/session_id:\s*(ses_[a-zA-Z0-9_-]+)/i)
-    if (taskMetadataSessionMatch) {
-      return taskMetadataSessionMatch[1]
-    }
-  }
-
-  const explicitSessionMatches = [...output.matchAll(/Session ID:\s*(ses_[a-zA-Z0-9_-]+)/g)]
-  return explicitSessionMatches.at(-1)?.[1]
+  return extractTaskLink(undefined, output).sessionId
 }
 
 export async function validateSubagentSessionId(input: {