feat(automation): post_comment action + Redis SETNX idempotency

[Musiker15]

Summary

Lands the post_comment automation action — the v1-scoped action that ADR 0010 deferred until the Redis idempotency claim was in place. Closes the third automation item from the v0.2.0-beta Deferred list.

⚠️ Crypto-relevant — please double-check. The automation-posted comment is encrypted client-side under the BoardKey, same as a human comment.

How it works

1. A rule like When card moved to Done → post comment "Closed on {{date}}.". The body template lives in enc_rule (server never sees it).
2. On trigger, the executor renders the template ({{date}} / {{datetime}} via split/join — no regex, no ReDoS, fixed token set), encrypts the rendered text under the BoardKey (bound to comment:new), and POSTs to /api/cards/[id]/comments.
3. Idempotency: the POST carries idempotencyKey = <ruleId>:<eventToken>. The server does SETNX automation:claim:<key> with a 60 s TTL. A lost race (racing tabs / retry) returns { deduped: true } — no duplicate comment. Redis hiccup → fail open (post the comment; a missed dedup beats a dropped comment).

Changes

• DSL (dsl.ts): post_comment added to ACTION_TYPES + ActionPostComment schema (body 1..2000 chars).
• Evaluator (evaluator.ts): evaluateAll now takes IdentifiedRule[] and tags each action with ruleId; new eventToken(event) builds the deterministic dedup discriminator.
• Executor (executor.ts): new ExecutorContext (encryptor + eventToken), post_comment case, pure expandTemplate helper.
• Comment POST route: optional idempotencyKey (charset-locked), Redis SETNX claim.
• Rule builder (automation-panel.tsx): action picker entry + comment textarea with a token hint; summary preview.

Security notes

• The comment is E2EE; the server stores only ciphertext, identical to a human comment.
• idempotencyKey charset is locked to [A-Za-z0-9:_-] so it can't smuggle anything into Redis. A forged key can at most suppress an automation comment for 60 s on a board the caller already has write access to — no cross-tenant impact (RBAC still runs in Comments.create).
• No-cascade invariant preserved: the executor posts via the REST API, never through the drawer, so a post_comment action can't re-fire a comment_added rule.

Tests

• automation-executor.test.ts — expandTemplate (5 cases incl. unknown-token passthrough)
• automation-dsl.test.ts — post_comment accept / empty-reject / over-cap-reject; action-list count bumped to 4
• automation-evaluator.test.ts — eventToken determinism + evaluateAll ruleId threading

39 automation cases green. pnpm typecheck + pnpm lint clean.

Test plan

• CI green
• Manual: rule "When moved to Done → post comment Closed on {{date}}", move a card, confirm one comment appears with today's date
• Manual: trigger the same rule twice quickly (or in two tabs) → still only one comment (SETNX dedup)
• Manual: confirm the posted comment is readable (decrypts) and the server DB row is ciphertext

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