Every Synapse event used to open its own service session, so two messages of
one Telegram chat landed in two unrelated chats. The dispatcher now returns a
`session_key` — derived from the payload according to the user's routing
document — and a later event carrying the same key joins the session that
opened it, within `reaction_session_ttl_minutes` of idle time (0 restores the
old always-fresh behaviour). A session that is still running is never joined:
`create_run` overwrites `state.run`, so a second run would orphan the first
one's subscribers — a busy thread gets a fresh session instead. When the
dispatcher names a different profile for the event, the session's profile is
switched through `set_profile`, never through `save()`, which does not rewrite
`name` or `profile_id`: the thread keeps its name and its history.

What the user reads in the transcript is now only the request. The event
record is a system message (`metadata.source == "synapse_event"`) drawn by a
new SynapseEventNotice.vue in the visual language of the recall badge, and the
framing plus the JSON envelope become a hidden user turn written once, on the
first event of a thread — not on every one. The instructions from Settings
reach the model through a new `current_reaction_instructions` ContextVar and
the `[Reaction session]` block of the system prompt, so they appear in no
transcript at all. The stored system record still has to reach the model, so
ContextBuilder's allowlist becomes `_LLM_SYSTEM_SOURCES = {task_note,
synapse_event}`.

The dispatcher gets a document of its own — how to route, rather than what to
do — stored beside the reaction instructions, versioned separately, and edited
in its own field in the settings panel. `synapse_instruction_versions` gains a
`doc` discriminator, so existing rows keep `'reaction'` and their history
verbatim. The new columns are added by `_MIGRATE`, and the index over `doc`
lives there too: `_DDL` runs first, so an index over a column the migration has
not added yet kills the whole batch on an existing database — which is what
the prod database is. A guard test keeps it that way.

Tests: 1776 passed, 1 skipped (backend), 242 passed (webclient, 28 files).

Settings is the first area off hard-coded English: 122 strings for the shell and
its five tabs — App, Account, Notifications, Synapse and MCP — plus the 43 the
shared vocabulary contributes (common.*, col.*, confirm.*, toast.*).

The English dictionary carries the very literals the templates used, so the
interface a test reads is byte-for-byte what it was and the 56 assertions on
English UI text stay green; only a slug that is genuinely counted had to be
restructured into a plural. In ru and uk the counted strings get the three
Slavic forms driven by n. Product names are never translated: Navi, Synapse,
MCP, Ollama, Tool call, Subagent and Token read the same in all three
languages, and the settings screen keeps one settings.* area with
panel-prefixed slugs rather than a slug per panel, as the other gnexus clients
do.

Strings carrying markup are split around it instead of hiding tags in the
dictionary: the install steps keep their inline icons and <code>http://</code>
in the template, with the words of each sentence on either side. Four lists of
labels — the settings tabs, two table headers, and the reaction options — are
now computed rather than module-level constants, since a list built at import
keeps the language that was active then and ignores a switch. Dates in the
panels go through the interface language as well, not the browser's.

Checked in Chromium against the built bundle: all three languages on all five
tabs, with a scan for a slug leaking into the rendered text as the pass
condition, and the account left with no override afterwards.

- sidebar: service-sessions toggle (special=true fetch replaces the
  regular list, active search drops out), muted style + robot icon on
  special items in the list
- settings: Synapse reactions panel — enable switch, completion push
  preference (always / only failures / never), notification destination
  (app / app+Synapse / Synapse, Synapse options disabled while no
  source key), reaction instructions editor with save + edit history
  (author and reason per version)
- stores: synapseReactions store; sessions store fetches respect
  showSpecial; getSessions passes special param
- vitest for api/session store/panel; dist rebuilt