feat(atlas): update resolvers and index for lineage-aware session resolution

- Update recent-model-resolver for session origin awareness
- Update resolve-active-boulder-session with lineage support
- Add comprehensive test coverage for boulder session resolution
- Add fallback tests for recent model resolver
- Update index tests for new lineage tracking

🤖 Generated with assistance of OhMyOpenCode

src/hooks/atlas/recent-model-resolver-fallback.test.ts

@@ -0,0 +1,72 @@
+declare const require: (name: string) => any
+const { describe, expect, mock, test, afterAll } = require("bun:test")
+import { mkdtempSync, mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { tmpdir } from "node:os"
+
+const testDirs: string[] = []
+const TEST_STORAGE_ROOT = join(tmpdir(), `recent-model-fallback-${Date.now()}`)
+const TEST_MESSAGE_STORAGE = join(TEST_STORAGE_ROOT, "message")
+
+mock.module("../../shared/opencode-storage-detection", () => ({
+  isSqliteBackend: () => false,
+}))
+
+mock.module("../../shared/opencode-message-dir", () => ({
+  getMessageDir: (sessionID: string) => {
+    const directPath = join(TEST_MESSAGE_STORAGE, sessionID)
+    return require("node:fs").existsSync(directPath) ? directPath : null
+  },
+}))
+
+afterAll(() => {
+  mock.restore()
+  while (testDirs.length > 0) {
+    const directory = testDirs.pop()
+    if (directory) {
+      rmSync(directory, { recursive: true, force: true })
+    }
+  }
+})
+
+describe("resolveRecentPromptContextForSession fallback ordering", () => {
+  test("uses JSON fallback ordered by time.created when SDK messages fail", async () => {
+    // given
+    const sessionID = "ses_recent_model_fallback"
+    const directory = mkdtempSync(join(tmpdir(), "recent-model-fallback-dir-"))
+    testDirs.push(directory)
+    const messageDir = join(TEST_MESSAGE_STORAGE, sessionID)
+    mkdirSync(messageDir, { recursive: true })
+    writeFileSync(join(messageDir, "msg_ffff0000_000001.json"), JSON.stringify({
+      agent: "atlas",
+      model: { providerID: "anthropic", modelID: "claude-sonnet-4-6" },
+      tools: { read: true },
+      time: { created: 10 },
+    }), "utf-8")
+    writeFileSync(join(messageDir, "msg_00000000_000999.json"), JSON.stringify({
+      agent: "atlas",
+      model: { providerID: "openai", modelID: "gpt-5.4" },
+      tools: { edit: true },
+      time: { created: 100 },
+    }), "utf-8")
+
+    const { resolveRecentPromptContextForSession } = await import("./recent-model-resolver")
+
+    const ctx = {
+      client: {
+        session: {
+          messages: async () => {
+            throw new Error("sdk ordering unavailable")
+          },
+        },
+      },
+    }
+
+    // when
+    const result = await resolveRecentPromptContextForSession(ctx as never, sessionID)
+
+    // then
+    expect(result.model).toEqual({ providerID: "openai", modelID: "gpt-5.4" })
+    expect(result.tools).toEqual({ edit: true })
+  })
+})