fix(showcase): path-based content-level starter-smoke probe

Rewrite the starter-smoke probe to the v2 path-based multi-route runtime
protocol the deployed starters actually speak (proven via a local
build+curl gate against examples/integrations/crewai-crews at 1.59.5):

- agent rung: GET /api/copilotkit/info -> 200 + version (was: any non-404)
- chat rung: POST /api/copilotkit/agent/<id>/run (Accept: text/event-stream)
  asserting >=1 TEXT_MESSAGE_CONTENT delta + terminal RUN_FINISHED + no
  RUN_ERROR (was: non-empty body)
- health rung: repointed to GET /api/copilotkit/info (the starters serve
  no /api/health route)
- interaction rung: GET / (unchanged)
- drop trailing slash on all runtime POSTs (the old /api/copilotkit/ 308s
  and drops the POST -> 404, the core cause of the red rung)

Plus a unified abort/body-read error classification (one abortOutcome()
helper keyed on the local externallyAborted flag): a self-timeout or a
non-abort error is transport-error (soft), only a genuine external abort
is 'aborted'; a cut-short body read softens to transport-error instead of
hard smoke-failed; the level loop short-circuits on external abort.

NOTE: the content-level chat rung will correctly read RED against the
deployed starters until the Python-side ag-ui-crewai RUN_ERROR (a
real-LLM, in-process agent failure, NOT a probe bug) is fixed.

Deferred follow-ups: verify the alert/staleness consumer branches on
errorClass (not state) so the soft/hard split is actually consumed;
res.text() resolve-partial precision edge; redirect:follow POST edge;
health/interaction body-drain; health/agent shared /info; CLASS_RANK
aborted-lowest; unmapped-starter columnSlug/prototype-key; test-coverage
gaps (resolveTimeoutMs, deriveStarterSlug, real-timer abort).

Author: jpr5

showcase/harness/config/probes/starter_smoke.yml

@@ -13,11 +13,21 @@
 #
 # Each driver invocation issues FOUR HTTP checks against the deployed base
 # URL and side-emits one row per smoke level plus an aggregate primary
-# (see drivers/starter-smoke.ts):
-#   - health      GET  `${base}/api/health`        → 200 + JSON body
-#   - agent       POST `${base}/api/copilotkit/`    → any non-404 response
-#   - chat        POST `${base}/api/copilotkit/`    → non-empty body (aimock)
-#   - interaction GET  `${base}/`                   → 200 (app shell serves)
+# (see drivers/starter-smoke.ts). The deployed starters mount the v2 runtime
+# in its default PATH-BASED `mode:"multi-route"` at `/api/copilotkit`, so the
+# checks dispatch by URL path (the dead single-route envelope POST to bare
+# `/api/copilotkit` is never issued):
+#   - health      GET  `${base}/api/copilotkit/info` → 200 (lightweight
+#                                                     runtime-mount liveness;
+#                                                     the starter has no
+#                                                     `/api/health` route)
+#   - agent       GET  `${base}/api/copilotkit/info` → 200 JSON carrying a
+#                                                     `version` field
+#   - chat        POST `${base}/api/copilotkit/agent/default/run`
+#                 (Accept: text/event-stream) → AG-UI SSE stream asserting ≥1
+#                 TEXT_MESSAGE_CONTENT delta + terminal RUN_FINISHED + NO
+#                 RUN_ERROR
+#   - interaction GET  `${base}/`                    → 200 (app shell serves)
 #
 # Rows emitted per invocation:
 #   - Primary `starter:<column-slug>`           aggregate { total, passed,