Severity routing

One Slack channel for the fleet. With 6+ codename agents firing every 20 minutes, everything ends up there: Lucius shipped, Drake noop, Bane no-coverage-target, automerge merged, cleanup swept, Gordon ECS-in-sync.

Two failure modes:

1. Drown the signal. A genuine alert (Claude rate-limit, ECS drift, security scan finding) gets lost in the daily firehose.
2. Split the channel. Two channels (one for noise, one for alerts) works, but one person plus two channels usually means neither gets read reliably.

Severity routing solves both without changing channel count.

The API

slack_post() takes an optional severity= keyword:

slack_post("Lucius shipped #42", severity="info")        # default: plain text
slack_post("Lucius hit max-turns on #42", severity="warn") # ⚠️ prefix
slack_post("Staging deploy drifted from main", severity="alert") # 🚨 + <!here>

Three tiers:

Tier	Behaviour	Use for
info (default)	Posted as-is	The bulk: agent shipped, merged, swept, no-op
warn	Prefixed ⚠️ if not already	Soft failures: rate-limit on one provider, max-turns hit, salvaged WIP draft
alert	Prefixed 🚨 + appends <!here>	Operator must see: production drift, fleet-wide rate-limit, doctor failure on a load-bearing agent, security signal

Unknown severity values are coerced to info. Existing callers without a severity= kwarg keep their previous behaviour exactly: back-compat default.

flowchart TB
    entry["slack_post(text, severity)"]
    sev{"severity"}
    info["post text as-is"]
    warn["prefix the warning glyph<br/>if not already present"]
    alert["prefix the alert glyph<br/>append the @here mention"]
    coerce["coerce unknown value to info"]
    webhook["POST to Slack incoming webhook"]

    entry --> sev
    sev -- "info (default)" --> info
    sev -- "warn" --> warn
    sev -- "alert" --> alert
    sev -- "anything else" --> coerce
    info --> webhook
    warn --> webhook
    alert --> webhook
    coerce --> webhook

What you get

In Slack, the channel timeline now reads like:

[normal]    ✅ Lucius shipped: <PR-url> (turns=46)
[normal]    📋 Drake firing complete (turns=15, cost=$1.20)
[normal]    Auto-merged 2 PR(s): <pr1>, <pr2>
[normal]    ✅ Lucius shipped: <PR-url> (turns=82)
[normal]    🧹 cleanup: swept 1 stale agent:in-flight claim
[bold]      ⚠️ Lucius #305 hit max-turns (150). Will retry.
[normal]    ✅ Lucius shipped: <PR-url> (turns=51)
[ping]      🚨 Gordon: staging deployment health
            ECS drift (live ≠ main): staging-api-service main=abc123 live=def456
            <!here>

Your eye snaps to the 🚨 line. The ⚠️ line is visible without scrolling. The ✅ flood is scannable peripherally.

Reclassification guidance

When sweeping a callsite, ask: what would I want to know about while making coffee?

• alert: anything that pauses the fleet, breaks production, or signals security. You should see it before the next agent firing can make it worse.
• warn: soft failures that recover on their own (rate-limit on one provider, max-turns on one issue) but should still be visible.
• info: everything else. If you’re not sure, this is the right answer.

Bias toward info. Over-using alert re-creates the firehose problem you started with.

What’s deferred

Today’s slack_post uses an incoming webhook. Webhooks have two limits:

• Cannot post threaded replies (no thread_ts).
• Cannot update the channel topic (read-only on channel state).

Bot-token posting exists in lib/slack_format.py for per-firing Block Kit threads. Two higher-level routing features remain follow-ups:

1. Daily-thread routing for info-tier. The fleet-recap-morning cron posts an anchor message at 07:30; every info post during the day goes as a threaded reply under it. Main-channel timeline shrinks to one anchor + the day’s warn and alert events.
2. Channel topic from fleet state. slack_set_channel_topic() renders e.g. Lucius: 17 ✅ / 3 ❌ today · Drake: 8 ok · 0 paused repos. Glanceable status without opening a dashboard.

Both tracked in Roadmap under “in-flight.”

See also

• Slack setup: webhook creation, AWS storage, optional bot-token path.
• docs/SLACK_SETUP.md: the full guide.
• agent_runner.slack_post: the source.