proto: widen error-on-paused for ADR 0013's auto-pause signal (1.3.0)

DAEMON's docs/adr/0013-task-state-machine-ownership.md needs a wire signal
for the difference between a paused task the daemon entered unilaterally
(auth_required, server_file_changed, disk_full) and one that was requested
(user, schedule, queue stop, admission reconcile) -- without it, DAEMON's §3
resume rule ("resume only when the reason matches the event that justifies
resuming") has nothing correctness-preserving to key on, and would have to
guess from timing. CORE has already accepted the ADR; this was the sole
remaining blocker per DAEMON's own status line on it.

No retype, no new field -- error was already TaskError | null on both
event.task.state and TaskSummary, exactly as DAEMON characterized the ask.
Only the *description* of when it is populated widens: previously "failed or
retry_wait", now also "paused, when the daemon entered it on its own
initiative". A deliberate pause still carries error: null. TaskError's own
top-level description gets the same widening, since it previously also said
"failed or retry_wait" and would otherwise contradict the field that embeds
it.

New fixture (event.task.state.auto-paused.json) exercises the case directly:
an auth_required pause with error populated, contrasted in its own
description against download.pause.json's error: null for a requested pause.
The existing event.task.state.json fixture's first assertion was stale
("error is present exactly when failed or retry_wait") and is corrected.

Minor bump, 1.2.0 -> 1.3.0: a description widening on an already-nullable,
already-optional field changes no JSON Schema shape, but it is a real
behavioral commitment change worth a version bump so downstream regenerates
and notices, per the same reasoning ADR 0010 applied to TaskErrorCode.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_012fgjnqFCS5h5L7gZTZo3rV

contracts/fixtures/events/event.task.state.auto-paused.json

@@ -0,0 +1,57 @@
+{
+  "name": "event.task.state \u2014 the daemon auto-pauses on a 401",
+  "description": "The CORE-auto-pause case ADR 0013 (docs/adr/) needs a wire signal for: the daemon paused this task on its own initiative -- not because the user clicked pause, a schedule window closed, or admission control reconciled a lowered cap -- and error explains why. Compare download.pause.json, where the same target state (paused) carries error: null because that pause was requested.",
+  "notification": {
+    "jsonrpc": "2.0",
+    "method": "event.task.state",
+    "params": {
+      "taskId": "8c1d4e5f-6a7b-4c8d-9e0f-1a2b3c4d5e6f",
+      "state": "paused",
+      "previousState": "connecting",
+      "summary": {
+        "taskId": "8c1d4e5f-6a7b-4c8d-9e0f-1a2b3c4d5e6f",
+        "filename": "film.mkv",
+        "saveDir": "/home/sami/Downloads/Video",
+        "url": "https://example.org/film.mkv",
+        "effectiveUrl": "https://example.org/film.mkv",
+        "sizeBytes": 1503238553,
+        "downloadedBytes": 0,
+        "state": "paused",
+        "speedBps": 0,
+        "etaSeconds": null,
+        "resumable": true,
+        "segments": 4,
+        "categoryId": "video",
+        "queueId": null,
+        "queuePosition": null,
+        "description": null,
+        "createdAt": "$isoDate",
+        "lastTryAt": "$isoDate",
+        "completedAt": null,
+        "error": {
+          "code": "auth_required",
+          "message": "the server asked for credentials (401)",
+          "httpStatus": 401,
+          "retryable": false,
+          "cause": null,
+          "attempt": 1,
+          "nextRetryAt": null
+        }
+      },
+      "error": {
+        "code": "auth_required",
+        "message": "the server asked for credentials (401)",
+        "httpStatus": 401,
+        "retryable": false,
+        "cause": null,
+        "attempt": 1,
+        "nextRetryAt": null
+      }
+    }
+  },
+  "assertions": [
+    "error is set here specifically because the daemon paused this task itself, not the user -- the trigger is event.auth.required on the same task shortly before",
+    "the scheduler must not resume this task on a schedule window or queue restart: only download.provideAuth (or the user explicitly resuming) may clear it -- resuming blindly re-fails immediately and looks like a flapping bug",
+    "a client distinguishes an auto-pause from a deliberate one by this field being non-null, not by inspecting previousState or any other heuristic"
+  ]
+}

contracts/fixtures/events/event.task.state.json

@@ -50,7 +50,7 @@
     }
   },
   "assertions": [
-    "error is present exactly when state is failed or retry_wait",
+    "error is present on every failed or retry_wait transition, and also on a paused transition the daemon entered unilaterally -- never on a paused transition the user or scheduler requested",
     "error.code is a TaskErrorCode, never a JSON-RPC ErrorCode \u2014 the two are different spaces",
     "retryable false means the scheduler will not pick this up again on its own"
   ]