Chat-surface correctness: persistent scheduled sends, frontend-scoped tools + prompts

[claudiusthebot]

Summary

Two chat-workflow fixes off main:

1. Scheduled messages survive restarts

send(..., delay_seconds=N) lived only in an in-process setTimeout. The model tells the user "reminder in 30 minutes", Talon restarts at minute 20, and the promise silently evaporates — the exact failure the "never promise without a mechanism" rule warns about, baked into the platform. Cron jobs survive restarts; scheduled sends now do too.

• Persistent store (storage/scheduled-store.ts): pending sends live in the kv table (scheduled.messages blob). The store is the source of truth; per-frontend timer maps are just the armed alarms.
• Persist-before-arm on Telegram and Discord schedule_message — a crash between the two steps is recoverable in that order, fatal in the other. Firing and cancelling clean up both store and timers.
• Restore on boot: when a frontend's action handler is created, persisted entries re-arm. Overdue entries fire immediately (late beats never); entries stale past 24h are dropped.
• cancel_scheduled also clears store-only entries (scheduled before a restart, no live timer).
• New list_scheduled tool (Telegram + Discord): schedule id, seconds remaining, text.
• Delay cap raised 1h -> 24h: with persistence, long delays are safe to honor.
• Bugfix en passant: delayed sends silently dropped buttons and reply threading on the tool side — the bridge now forwards rows + reply_to_message_id, and the fire path replays them.

2. Frontend tool servers scoped to the chat's owning frontend

With frontend: ["telegram", "native"], every chat registered a tool server per configured frontend — a native-app conversation saw mcp__telegram-tools__* alongside native-tools in its tool list. Confusing in the client UI, and an invitation to deliver a reply to the wrong surface.

New shared frontendsForChat(chatId, configured) infers the owning frontend from the chat-id shape (native d_*, teams teams_chat_*, discord discord_*, telegram numeric — the same convention the gateway uses to route actions) and scopes the server list to exactly that frontend. Cross-surface contexts (heartbeat sentinel, one-shot cron, terminal sessions) keep the full set on purpose — they reach any surface via explicit chat_id. Applied in claude-sdk, codex, and openai-agents; the kilo/opencode remote-server path already binds a single frontend per server instance.

3. Per-chat frontend prompt flavour

Companion to #2, one level deeper: the system prompt itself was built once for frontends[0], so a native-app chat received the full Telegram platform prompt (telegram.md guidance, Telegram reaction lists) — native.md was never rendered for it. The per-session snapshot layer now resolves the chat's owning frontend and builds that flavour, frozen per session as before. Non-primary flavours are built purely — without mutating the global config prompt — so a native chat starting a session can't clobber the prompt other readers consume. Cross-surface contexts fall back to the primary flavour.

4. Per-chat frontend for delivery contracts + remote-server tools

Completes the sweep across every backend. The delivery contract and [FLOW VIOLATION] reminder template the frontend's actual tool names (native's send tool is send_message, telegram's is send) — built for the process-primary frontend, native chats got a contract instructing send(...), which after #2 doesn't even exist in their toolset. claude-sdk + openai-agents resolve the contract frontend per chat; codex/opencode/kilo suffix constants become per-frontend builders applied per chat; and the kilo/opencode remote-server path now binds each chat's owning frontend instead of state.frontendName for all chats.

Test plan

• New scheduled-messages.test.ts (9 tests, per-test TALON_DB_PATH isolation + fake timers): store CRUD/ordering, schedule->fire->cleanup, cancel with a live timer, cancel of a store-only (pre-restart) entry, per-chat listing, restore re-arm, overdue immediate fire, stale drop, cross-frontend isolation.
• New frontend-scoping.test.ts: chat-id classification per frontend, owned-chat scoping, heartbeat/terminal full-set fallback, owner-not-configured fallback.
• Extended shared-system-prompt.test.ts: native chat gets the native flavour with no global rebuild, telegram chat keeps the primary path, heartbeat falls back, flavours freeze independently per session.
• Full CI validates typecheck, lint, and the untouched surfaces.

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