feat(cat): answer @cat in private messages

[catomean]

Tagging the Cat in a conversation now gets an answer in that conversation, from the Cat's own account.

Shape: a queue with two payers

The write path records that a reply is owed and returns — an LLM round trip must not sit inside the sender's POST. A worker pays the debt.

The systemd timer is the durability path, not the latency path: the write also kicks a run, so a reply normally lands in seconds. The tick is what guarantees the question survives a process dying mid-thought. An assistant that silently drops a question is worse than one that's slow.

property	mechanism
one mention → one reply	UNIQUE (source_type, source_id); 23505 treated as success, which is what makes an at-least-once producer safe
two workers never collide	FOR UPDATE SKIP LOCKED in claim_cat_mentions
a failed attempt retries	back to pending until MAX_ATTEMPTS, then failed with the reason kept

Concurrency proven on production with two simultaneous sessions:

seeded: 2
A claimed: 1
B claimed: 1
distinct rows claimed: 2 of 2
still pending: 0
cleaned up: 0

The bug I wrote and caught

The dedupe key must be the message id. My first draft fell back to the conversation id when no message id was passed — which would have meant the first question ever asked in a conversation was the only one ever answered, every later insert colliding with the unique constraint and reading as "already queued".

The parameter is now required, the fallback is gone, and a test fails if it comes back.

"@cat what do you think about this?"

That works because "this" means the conversation. The Cat reads CAT_CONTEXT_MESSAGE_WINDOW recent messages of the thread it was tagged in — no other conversation, no history beyond the window. That's a stated promise about what tagging consents to, which is why the number lives in config rather than inside a query.

Two product calls, taken as documented assumptions since they were open and both are reversible:

• The Cat stays in the conversation once tagged — a follow-up needs no second tag, both people can see it's present, and it can be removed like any participant.
• A failure to think is still answered. CAT_FALLBACK_REPLY goes out rather than nothing, because a tag that produces silence is indistinguishable from a broken feature — and this codebase has shipped exactly that before.

Layering

parse (pure)  →  resolve (one query)  →  note (the seam a write path calls)
              →  queue (durability)   →  worker (dispatch)  →  reply (what it says)

Nothing was added to chat-orchestrator.ts or memory.ts — already 837 and 1062 lines. A new surface (wall posts, group chat) gains all of this by calling noteCatMention.

Verification

• npm run verify — exit 0 (2359 tests); check:rpc-exists picked up claim_cat_mentions, baseline still zero
• 10 new tests, including the dedupe-key regression and "never throws — a person's message must be stored whatever the Cat does"
• migration dry-run inside BEGIN … ROLLBACK, plus the live concurrency test above

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