S00-003: Record blocked task and remediation handoff

Changes: Preserve incomplete work and blocker metadata for S00-003. This checkpoint does not mark implementation accepted.
Validation: Session ended with status blocked.
Blocker: S00-003 cannot attest parser limits: Stanza 12.22.1 exposes no resource bounds and its persistent WebSocket parser accepts large/deep XML and reassembles incomplete documents across separate input messages.

Task: S00-003
Agent: auto-protocol-902594b44429
Role: protocol
Action: claim
Status: blocked

Task title: Проверить XMPP WSS/auth библиотеку

planning/tasks.json

@@ -268,7 +268,8 @@
       "depends_on": [
         "S00-001",
         "S00-002",
-        "S00-017"
+        "S00-017",
+        "S00-018"
       ],
       "requirements": [
         "ACC-004",
@@ -995,6 +996,65 @@
       ],
       "context_budget_chars": 48000
     },
+    {
+      "id": "S00-018",
+      "stage": "S00",
+      "kind": "blocker",
+      "root_task": "S00-003",
+      "blocker_depth": 1,
+      "unblocks": [
+        "S00-003"
+      ],
+      "role": "protocol",
+      "reviewer_role": "security",
+      "title": "Validate bounded standalone XML ingress for the XMPP candidate",
+      "outcome": "One isolated runnable and independently reviewed ingress experiment enforces explicit finite XML resource limits and standalone text XML per WebSocket message before unsafe accumulation/import, through a supported library integration path.",
+      "depends_on": [
+        "S00-001",
+        "S00-002",
+        "S00-017"
+      ],
+      "requirements": [
+        "ACC-004",
+        "NET-003",
+        "NET-004"
+      ],
+      "scope": [
+        "experiments/0002-xmpp-library/parser-validation/**",
+        "docs/decisions/0002-xmpp-parser-validation.md"
+      ],
+      "inputs": [
+        "docs/WEB_PROFILE.md",
+        "docs/ARCHITECTURE.md",
+        "docs/CONTRACTS.md",
+        "docs/TESTING.md",
+        "roles/protocol.md",
+        "docs/decisions/README.md",
+        "state/blockers/S00-018.md"
+      ],
+      "spec_sections": [],
+      "ui_sections": [],
+      "steps": [
+        "Read original blocker evidence, bounded probe, shipped parser/transport APIs and RFC 7395 framing; reproduce the stock failure with finite synthetic input.",
+        "Choose and document a supported ingress integration using vetted existing XML parsing; keep limits experiment-local, do not implement a handwritten security XML parser or patch ignored vendor sources.",
+        "Enforce byte/depth/element/attribute budgets and complete single-document text-message framing before unbounded tree/import work; reject invalid input terminally and clear attempt state.",
+        "Add valid boundary and adversarial fixtures including incomplete messages, multiple roots, oversized tokens/attributes, deep XML, malformed XML and binary messages; verify rejection causes no stanza delivery or retained cross-message state.",
+        "Record exact dependencies/licenses/browser API constraints if adding packages, runnable commands/results and limitations, then submit for independent security review."
+      ],
+      "acceptance": [
+        "Explicit finite byte/depth/element/attribute budgets are enforced before uncontrolled accumulation/import; boundary-valid stanza still parses with actual library behavior.",
+        "Each WebSocket message is one complete standalone text XML document; incomplete/multiple-root/binary input is rejected and cannot be revived by a later message.",
+        "Original large/deep/cross-message failure categories are rejected under documented local limits without post-import-only checks, vendor patch or TLS/CORS bypass.",
+        "One supported integration path and cleanup/reset behavior are demonstrated by runnable actual ingress tests; no production shared contract, auth policy or product limit change."
+      ],
+      "checks": [
+        "Positive boundary-valid framed stanza using the actual candidate registry/parser and ingress integration.",
+        "Original bounded probe categories exceed local budgets or fail framing and produce terminal rejection without stanza emission.",
+        "Malformed/unfinished/multiple-root/binary/oversized-token/attribute/depth/element cases; no cross-message retained state or late revival.",
+        "Fresh attempt/reset accepts valid input; dependency pin/license/API and scope inspection."
+      ],
+      "context_budget_chars": 48000
+    },
     {
       "id": "S00-010",
       "stage": "S00",