test(subagent-sdk): keyless Loader-composition e2e across the SDK wire

A test-only cordis.yml under examples/jsonrpc-agent boots the headless app
through the Loader; a scripted model delegates once to the SDK backend, whose
child is a COMPLETE second harness runtime (own cordis.yml, jsonrpc serving
surface, scripted cwd-echo model, own JSONL persistence). Asserts the parent
tool result AND the child's own persisted transcript both carry the parent
session's workspace cwd; child launch resolves through the shared
example-launch resolver so src/lib modes both hold.

knip.json

@@ -36,6 +36,9 @@
         "tui-agent/tests/fixtures/tui-scripted-llm.ts",
         "acp-agent/tests/fixtures/subagent/subagent-acp/mock-delegating-llm.ts",
         "acp-agent/tests/fixtures/subagent/subagent-acp/driver.ts",
+        "jsonrpc-agent/tests/fixtures/subagent/subagent-sdk/driver.ts",
+        "jsonrpc-agent/tests/fixtures/subagent/subagent-sdk/child-mock-llm.ts",
+        "jsonrpc-agent/tests/fixtures/subagent/subagent-sdk/mock-delegating-llm.ts",
         "*/tests/**/*.e2e.ts",
         "*/tests/**/*.snapshot.ts"
       ],
@@ -262,8 +265,14 @@
       ]
     },
     "packages/session-query/session-query-sqlite": {
-      "entry": ["tests/**/*.spec.ts", "tests/**/*.e2e.ts"],
-      "project": ["src/**/*.ts", "tests/**/*.ts"]
+      "entry": [
+        "tests/**/*.spec.ts",
+        "tests/**/*.e2e.ts"
+      ],
+      "project": [
+        "src/**/*.ts",
+        "tests/**/*.ts"
+      ]
     },
     "packages/code-runtime/code-runtime-worker": {
       "entry": [
@@ -316,8 +325,14 @@
       ]
     },
     "packages/session-persistence/session-checkpoint-policy": {
-      "entry": ["tests/**/*.spec.ts", "tests/**/*.e2e.ts"],
-      "project": ["src/**/*.ts", "tests/**/*.ts"]
+      "entry": [
+        "tests/**/*.spec.ts",
+        "tests/**/*.e2e.ts"
+      ],
+      "project": [
+        "src/**/*.ts",
+        "tests/**/*.ts"
+      ]
     },
     "packages/util/paths": {
       "entry": [