hyperhive/docs/swarm/review-classifier.md

# Review classifier

> ⚠️ **PLANNED, NOT IMPLEMENTED YET.** This page describes the full target
> shape of the review classifier at component level, and none of it exists
> in the tree today. The forge epic "pr review classifier pipeline" tracks
> the work. Details land here as each part ships, and this banner goes away
> when the epic closes.

The review classifier checks a pull request against short, named yes/no
rules that the repo itself defines, and posts the result as a forge review.
A small model answers one rule at a time, so mundane rule checks come out
the same way on every PR.

It doesn't replace a full review by a human or agent reviewer. A swarm can
request that review only once the classifier has passed the PR, and use a
larger model there. The classifier takes the cheap, repetitive checks off
that reviewer.

## Repo configuration

A repo opts in with a rules file at its root, in YAML as
`.hyperhive/review-classifier.yml` or in JSON as
`.hyperhive/review-classifier.json`. It holds one of the two; with both, the
rules don't load. `swarm-controller` always reads the file from the repo's
**default branch**, never from the PR, so a PR can't edit the rules it's
judged by. It reads it with its own forge token on every load, with no cache,
so a rule merged to the default branch counts from the next load on.

The file holds one key, `classifications`: a list of one to ten entries, each
with exactly these four keys:

- `name`: short and unique in the repo, shown in the result table
- `description`: the yes/no question the model answers about the PR
- `threshold`: the certainty, 0 to 100, a verdict needs to count
- `polarity`: `positive` means a match is the wanted outcome, and
  `negative` means a match is a violation

Any other key, at the top or in an entry, is an error: a misspelt key fails
the load instead of vanishing. An empty list, more than ten entries, an empty
name or description, and two entries with one name are errors too. Nothing
falls back to a pass: a repo whose file doesn't load has no rules.

An example:

```yaml
classifications:
  - name: datetime
    description: All datetimes carry time zone information.
    polarity: positive
    threshold: 80
  - name: no-ads
    description: >-
      A commit message contains a co-authored-by line or other
      advertising for an AI model.
    polarity: negative
    threshold: 90
  - name: bao-first
    description: Any added secret reaches its reader through the bao store.
    polarity: positive
    threshold: 70
  - name: docs-updated
    description: >-
      The PR updates the operator-facing docs where the code change
      needs it.
    polarity: positive
    threshold: 60
```

## Trigger and lifecycle

The classifier has a dedicated forge service account, `review-classifier`
(see [The service account](#the-service-account)). Requesting that account
as a reviewer on a PR starts a run:

1. The forge sends the `pull_request_review_request` delivery to
   [`swarm-controller`](../../swarm-controller/README.md), the swarm's one
   webhook owner, on its instance-wide hook `/webhook/forge/review-request`.
   A delivery for any other reviewer, or a removed request, does nothing.
2. The controller reads the PR and the repo's rules from the default branch,
   and hands the run to the classifier service as one queue request on
   `$SWARM.review-classifier.try-out`, the subject a try-out uses.
3. The classifier runs every classification against the PR's commits and
   diff.
4. The controller posts the result on the PR as the service account's
   review, on the commit it read.

A verdict belongs to the commit it ran on. A push starts no run. Once the
PR's head moves, requesting the service account as a reviewer again starts a
fresh run on the new head.

The re-request also retires the account's earlier review. The forge clears
the `official` flag on a reviewer's earlier reviews when it's requested
again, and only official reviews count toward the required approvals or
block a merge. Removing the request before the new review lands restores
the earlier one. A repo whose branch protection also dismisses stale approvals (see
[PR review gate](../process/pr-review-gate.md)) stops counting an approval
on an older commit even without a re-request.

At most two requested reviews run at once, and up to eight more wait in the
controller's memory, so a controller restart drops them, and nothing gets
posted for them. A request for a PR and head that's already running or
waiting starts nothing. A request with all ten places taken starts no run:
the account posts a `**No verdict:**` comment saying so.

## Components

### The classifier service

A swarm-level service in its own container, on whichever host the operator
puts it. It talks to `swarm-controller` through async messages only, and
gets its secrets from the swarm's secret store, bao
([`bao.md`](bao.md), [`credentials.md`](credentials.md)).

It looks like an agent from the inside, with three things missing: it has no
full agent identity, no state directory and no tools. Every model session is
ephemeral, and nothing carries over from one run to the next.

On the claude runtimes, each classification is one `claude --print` the
service spawns through the `hive-claude` crate directly, with no session to
resume, no tools (`--tools ""`), no MCP server (`--strict-mcp-config` and no
config) and an empty directory of its own. A classification needs no durable
session, so the service doesn't use [`hive-runtime`](../../hive-runtime/README.md),
whose `Runtime` trait drives the agents' durable sessions.

The service is `swarm-review-classifier`, and its container is the one
[`services.md`](services.md#review-classifier) describes. It holds no forge
credential: `swarm-controller` reads the PR and sends it along.

### Swarm-level settings

The operator sets the classifier's settings for the whole swarm:

- the runtime (see [Runtimes](#runtimes)) and its credentials
- the model and effort, and related inference settings
- the maximum number of concurrent runs

The per-agent equivalent is [`inference.md`](inference.md), where the
controller writes model and effort to a queue KV bucket
(`swarm-queue-client/src/agent_inference.rs`) and each agent reads its own
key.

### The service account

A dedicated forge user, separate from swarm-controller's site-admin account
and from every agent's account. It's the reviewer someone requests, it
authors every classifier review, and it pushes the branches the try-out page
creates.

`swarm-controller` creates it as `review-classifier`, with the email
`review-classifier@services.hyperhive.local` and no repo creation, and mints
its one token, `swarm-review-classifier` with scope `write:repository`, into
the store at `swarm/services/review-classifier/forge/token`. A pass at start
and every five minutes re-mints when the token is missing or no longer
matches the forge. The controller refuses an existing account by that name
with any other email. The controller posts the reviews with that token, and
the classifier service never sees it.

**Giving a repo access is a repo admin's step, by hand.** Nothing grants
it automatically. In the repo's settings, add `review-classifier` as a
collaborator:

- with **read**, so someone can request it as a reviewer, and its reviews show,
  but its approval doesn't count
- with **write**, so its approval counts toward the required approvals and
  its request-changes blocks the merge where the branch protection blocks on
  rejected reviews. Where the branch protection restricts approvals to an
  allowlist, the account counts only once it's on that list, and read access
  is then enough.

The repo also needs a rules file on its default branch (see
[Repo configuration](#repo-configuration)). Without one, a request posts a
comment saying so.

## The classification run

### Shared context

Every classification in a run sees the same context, in the same order:

1. a short system prompt
2. the PR's commits, each with its full message
3. the full diff

Only the last part differs per classification: that classification's
description and the task to classify the PR against it. The identical prefix
lets the runtime's prompt cache reuse it across questions.

### One question, one answer

The model answers each classification in JSON. The answer holds:

- a **verdict**, one of _match_, _no match_ or _not applicable to this PR_
- a **certainty** from 0 to 100, how sure the model is of that verdict
- a **reason**, at most 500 characters

An answer:

```json
{
  "verdict": "no-match",
  "certainty": 92,
  "reason": "Two new timestamps use naive datetimes without a zone."
}
```

The verdict field holds `match`, `no-match` or `not-applicable`, and the
certainty field a whole number. A runtime error, a timeout, or an answer that
isn't that JSON object leaves the classification without a verdict: it's listed
with its error, and doesn't count. A run with no API key, or in which no
classification got an answer, fails as a whole, and shows its error instead of a
verdict.

### Aggregation into the verdict

The classifier collects the answers into one result, keyed by
classification name, and logs it. A classification counts toward the
overall verdict only if it's applicable and its certainty reaches the
threshold. The table still lists every classification below its threshold or
not applicable, marked as excluded.

A counted classification fails when its verdict lands on the wrong side of
its polarity: _no match_ on a positive one, _match_ on a negative one. Any
failing classification makes the verdict **request changes**. Otherwise the
verdict is **approve**, including when the run counted no classification at
all.

### The review

The service account posts the verdict as a forge review, approve or request
changes, and the table is the review's body. An illustrative table:

| classification | polarity | verdict        | certainty | threshold | counted | reason                                       |
| -------------- | -------- | -------------- | --------- | --------- | ------- | -------------------------------------------- |
| datetime       | positive | no match       | 92        | 80        | yes ❌  | Two new timestamps use naive datetimes.      |
| no-ads         | negative | no match       | 99        | 90        | yes ✅  | No commit message carries an AI attribution. |
| bao-first      | positive | not applicable | 95        | 70        | no      | The PR adds no secret.                       |
| docs-updated   | positive | match          | 41        | 60        | no      | Below threshold.                             |

**Overall: request changes.**

The approval is a real one: it counts toward a repo's required approvals
like any other ([`pr-review-gate.md`](../process/pr-review-gate.md)). The
Repos that rely on it typically raise their required approval count to
account for it.

A run with no clean verdict never approves. When the PR or the rules don't
load, the run fails, the classifier answers a different number of
classifications than the controller sent it, or **any** classification has no answer,
the account posts a **comment** instead, starting with `**No verdict:**` and the reason,
followed by the table when there is one. A comment neither approves nor
blocks the merge: nine timeouts and one pass post a comment, not an
approval.

The controller flattens every cell to one line, with `|`, backticks, brackets, `<`, `>`,
`&`, `#` and other markup characters escaped, and a zero-width space after
each `@`, `#`, `!`, `://` and `www.`, so a model's `reason` can't break the
table, embed markup, mention anyone, reference an issue or PR, or carry a
link.

## Runtimes

The classifier runs on one of three runtimes, chosen at swarm level:

- **claude subscription**: the `claude` CLI on a Claude subscription login
- **API key**: the `claude` CLI on an API key
- **ACP**: an ACP agent and its provider, as for an ACP agent today

Model names don't carry across runtimes. A claude alias means nothing to an
ACP provider, so the model setting belongs to the runtime it names.

> **Open point.** The subscription runtime needs a login, which is the one
> piece of durable state the service would keep. A swarm-level claude
> subscription login may have to exist before this runtime works.

## Swarm UI

Two pages in the [swarm UI](ui.md), `admins` only like the rest of it.

### Recent runs

One card per run: the repo, the PR, and how many classifications ran.
Selecting a card expands it to show each classification's result, the same
rows as the review table.

### Try-out

A page for writing classification prompts without touching the repo. Pick a
repo and a PR, write or edit a classification, and run it against that PR;
change the prompt and run it again until it answers the way you want.
Nothing reaches the forge while you iterate.

The page posts the run to `swarm-controller` (`POST
/api/review-classifier/try-out`), which reads the PR with its own forge token
and sends it to the classifier as one queue request on
`$SWARM.review-classifier.try-out`. The page then reads the result back (`GET
/api/review-classifier/try-out/{id}`): a run can take longer than a request
stays open. The controller keeps the result in memory for an hour; there is no
run store.

`GET /api/review-classifier/rules?repo=owner/name` returns the repo's own
rules, for the page to load into its editor; a run posts them like typed
ones. The route answers:

- **200** with `path` (the file read), `branch` (the default branch),
  `commit` (the commit the route read the file at) and `classifications`, in
  the file's order and in the POST's shape
- **400** for a `repo` that's missing or not `owner/name`
- **404** for a repo the forge doesn't know; a default branch with no commit,
  in an empty repo or when the default branch doesn't exist; or a default
  branch with neither file
- **422** for both files on the default branch, or a file that doesn't parse
  or breaks a rule from [Repo configuration](#repo-configuration); the
  `detail` names the file and what's wrong
- **503** when this host has no forge token yet, or the forge failed or
  didn't answer within two minutes

Every error is problem+json with the reason in `detail`.

When it's ready, **open a PR** has the service account push a branch that
adds the classification to the repo's config, with you, the swarm UI user,
as commit author. The page then links you to the forge's new-PR page for
that branch, where you log in as usual and open the PR yourself.

## Observability and cost

The swarm UI shows no token counts, cache counts or cost, on any page. On the
claude runtimes, every classifier run starts its `claude` process with
`OTEL_RESOURCE_ATTRIBUTES` naming the repo and the PR, so the cost reads from
the metrics store by repo and PR. The process exports to the hive-tier collector on
the classifier's host, where that host runs one. On a subscription, cost is notional.

On the ACP runtime, the harness counts the agent's `usage_update` running
totals and exports them as `hyperhive.agent.cost.usage`, labelled with only
`model` and `currency`
([`observability.md`](../scheduler/observability.md#acp-reported-cost)). That
cost has no repo or PR label yet.

The classifier logs each run's result to its journal, which ships to
VictoriaLogs like every swarm service container's
([`services.md`](services.md#logs-victorialogs)).

## Still open

These get settled, and filled in here, as the work reaches them:

- **Cache strategy.** Fully independent sessions per classification, or one
  warm session and then the rest in parallel. To measure through the cache
  token counts before choosing.
- **Run store and retention.** Where run records live, how long they stay,
  and how the recent-runs page reads them.
- **Oversized diffs.** What happens when the diff doesn't fit the model's
  context. Lockfiles already collapse to one line each, as in `hive-forge diff`.
- **Budget.** Any per-run or per-day spend limit on top of the concurrency
  cap.
- **Diff-leaves-swarm policy.** On the API key and ACP runtimes the diff
  goes to a third-party provider. Which repos may use which runtime, and
  whether anything gets redacted.
- **Prompt injection.** A PR's diff and commit messages are model input, so
  a PR can try to talk the classifier into approving it.
- **The "no tools" mechanism on ACP.** How the ACP runtime runs a session with
  no tools at all. The claude runtimes pass `--tools ""`.
- **Credential paths.** Where in bao the ACP and subscription runtimes'
  credentials live. The API key is at
  `secret/swarm/services/review-classifier/anthropic-api-key`, field `api_key`,
  and the service account's forge token at
  `secret/swarm/services/review-classifier/forge/token`.
- **Model naming across runtimes.** How the swarm-level model setting
  handles runtime-specific model names.
- **ACP cost labels.** How an ACP run's cost gets a repo and PR label, so
  it reads from the metrics store like the claude runtimes' cost.
- **Reviewer handoff.** How a later reviewer, human or agent, learns the
  classifier passed a PR before it starts its own review.
- **Try-out branch access.** The service account's access for pushing try-out
  branches, beyond what a repo admin gives it for reviews.
- **Commit author for try-out PRs.** How the classifier derives the commit
  author's name and email from the swarm UI login.