feat: harden support, localize knowledge and add operator availability [skip ci]

Source-only publication of reviewed commit 64e96a7f423673dc29ad56485be9fc79bce8af1c.

Passed in isolation: focused frontend/backend tests, race checks, TypeScript typecheck, lint, Go compilation, Flowgram build, and deterministic SDK build/tests.

Not accepted as a production release: Next.js export/native assembly remains blocked by environment memory limits; browser interaction and MySQL staging acceptance remain unverified. No production server, database/schema, runtime configuration, deployment, release tag, or workflow execution was performed.

Expected source tree: 0a4a7528e9.

AGENTS.md

@@ -273,3 +273,25 @@ Before handing off a change, confirm the applicable items:
 - Generated files were regenerated from their source and were not manually edited.
 - Relevant tests/typechecks/lint/build/browser checks were run, and any validation limitation is reported.
 - `git diff --check` passes and unrelated worktree changes remain untouched.
+
+
+## Independent hardening fork boundaries
+
+Modified in this independent fork. Preserve the upstream license and existing
+notices. Public history begins from a source snapshot, not the upstream Git
+history. See docs/hardening/README.md for the source revision and release gate.
+
+- Treat canonical customer/channel identity, scoped issuer proof, live-session
+  revalidation and permission-filtered WebSocket delivery as security invariants.
+  Never restore raw external-ID topic routing or unscoped public identity lookup.
+- Old customer tokens and legacy identity reconciliation have explicit upgrade
+  implications. Do not auto-merge legacy customers or delete history to make a
+  migration pass; follow docs/hardening/CUSTOMER_IDENTITY_UPGRADE.md.
+- Setup repair previews must bind exact named changes to the caller and current
+  state. Apply requires explicit matching approval and transactional writes.
+  Never resurrect deleted configuration or silently create working schedules.
+- Keep editor drafts, sends and delayed async responses bound to their captured
+  identity and conversation. Clear only the sent draft revision after success.
+- Maintain Russian alongside English and Chinese for every changed UI/API string.
+- Keep docs/hardening/VALIDATION.md accurate. Tests authored but not executed are
+  not passing tests; source parsing is not a build or browser acceptance check.