# 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.

How many requested reviews run at once is a swarm-wide setting, two by
default (see [Swarm-level settings](#swarm-level-settings)). Up to eight more
wait in the controller's memory, a bound that isn't configurable, so a
controller restart drops them, and nothing gets posted for them. Waiting
reviews start in no guaranteed order. A request for a PR and head that's
already running or waiting starts nothing. A request with every running place
and all eight waiting 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 model, the effort and how many requested reviews run at once are one
document for the whole swarm. `swarm-controller` keeps it in its
`review-classifier-settings` KV bucket under the key `all`, and no other
service reads it. With no document stored, the classifier runs on `haiku` at
claude's default effort, two reviews at a time. The controller
ignores a stored field it doesn't know, and a document it still can't decode
counts as none, with a warning in its log, until the next PUT replaces it.

`GET /api/review-classifier/settings` answers the settings in force.
`PUT /api/review-classifier/settings` replaces them whole and answers what it
stored. Both take and give one shape:

```json
{ "model": "haiku", "effort": null, "max_concurrent_reviews": 2 }
```

- `model`: the model every classification runs on, as claude's `--model`
  takes it: one word with no whitespace, not starting with `-`
- `effort`: `low`, `medium`, `high`, `xhigh` or `max`; `null`, or left out of
  a PUT, passes no `--effort`
- `max_concurrent_reviews`: 1 to 8, how many requested reviews run at once.
  Try-outs don't count toward it. Up to eight more reviews wait for a place

The controller reads the settings for every run and sends the model and
effort in the run request, so a change applies from the next run with no
restart. A try-out reads them when it's posted, a review when it gets its
place. Lowering the limit lets the runs already going finish. A run request
with no model runs on `haiku`.

The PUT needs the `Remote-User` header the gateway sets, as the try-out POST
does. Every error is problem+json with the reason in `detail`:

- **400** for a body that isn't JSON or isn't this shape (a missing `model`
  or `max_concurrent_reviews`, an unknown field, an effort outside the five
  levels, a `max_concurrent_reviews` that isn't a whole number), an empty
  `model`, one with whitespace or one starting with `-`, or a
  `max_concurrent_reviews` outside 1 to 8
- **401** for a PUT with no `Remote-User`
- **503** when this host has no swarm queue, or it isn't connected
- **500** when the controller can't read or write the settings

When the controller can't read the settings, a try-out answers the same 503
or 500, and a review posts a no-verdict comment. The runtime (see
[Runtimes](#runtimes)) isn't a setting yet, and the operator writes the API
key by hand in the secret store
([`services.md`](services.md#review-classifier)).

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, and the
finished run goes into the [run store](#run-store-and-retention).

`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

The page's repo and PR fields offer values to pick from, and stay free text,
since a run also works on a merged or closed PR. Two routes feed them:

- `GET /api/pulls/repos` lists the repos with at least one open PR, as
  `owner/name`.
- `GET /api/pulls?repo=owner/name` lists the repo's open PRs, highest number
  first, each with `number`, `title` and `head_sha`. It answers **400** for a
  `repo` that's missing or not `owner/name`, **404** for a repo the forge
  doesn't know, and **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.

## Run store and retention

`swarm-controller` records every run when it ends: a try-out when the
classifier's reply arrives, a requested review once the controller has posted
its review or the post has failed, and a request turned away because the
queue was full once its comment is on the forge or the post has failed. A review request for a head that's already
running or waiting starts nothing and isn't recorded. A run still going isn't
in the list, and a controller restart drops a run in progress.

The newest 100 runs are one JSON array under the key `recent` in the
`review-classifier-runs` KV bucket on the swarm queue, which only the
controller reads or writes. The controller creates the bucket on first use and
adds each run with a compare-and-set write, so the list survives a controller
restart or a move to another host. Recording the 101st run drops the oldest;
there's no time-based retention. The controller leaves a run it can't decode, such
as one a newer build recorded, out of the list with a warning in its log. It
keeps the run in the store as it was and counts it toward the 100. A document
that isn't a list reads as no runs. The controller logs a failed write, and it
changes nothing on the forge.

`GET /api/review-classifier/runs` returns the list, newest first. Like the
try-out GET, the gateway's `admins` rule gates it, and the controller checks no
header. Each run has:

- `id`: a try-out's is the id its POST answered with
- `trigger`: `try-out` or `review`
- `repo` (`owner/name`), `pr`, and `requester`: the swarm UI user who started
  the try-out, or the forge user who requested the review
- `head_sha`: the commit the run read, absent when the PR wasn't read, as for
  an unreadable PR or a full queue
- `started_unix` and `finished_unix`: a try-out starts at its POST, a review
  once it has a run place
- `outcome`: `approved`, `changes-requested`, `no-verdict`, `queue-full` or
  `post-failed` for a review; `done` or `failed` for a try-out
- `detail`: the reason, for every outcome but `approved`,
  `changes-requested` and `done`. For `post-failed` it's the run's own reason,
  when it has one, then why the post failed.
- `rows` and `overall`, as the try-out GET returns them, when the classifier
  answered
- `review_url`: the posted review, when the forge names its URL

A run holds no diff, no commit text and no token count or cost. The route
answers 503 when the controller has no swarm queue or can't reach the bucket,
and 500 when it can't read the list, both as problem+json.

Each recorded run is also one `info` event from `swarm-controller` with the
message `review classifier run finished`. The event carries the same fields,
with `rows` as JSON. It reaches VictoriaLogs through the host journal, where
each field arrives as `F_` and the name in capitals (`F_OUTCOME`, `F_REPO`), so
a run whose write failed is still there:

```console
$ swarm-logs query '_time:7d _SYSTEMD_UNIT:="swarm-controller.service" _msg:="review classifier run finished" | fields _time, F_TRIGGER, F_REPO, F_PR, F_OUTCOME, F_DETAIL, F_REVIEW_URL' --format json
```

Add a filter such as `F_OUTCOME:="post-failed"` before the `|` to narrow it.

## 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.
- **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.