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docs/rfcs/0005-event-vocabulary.md
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— RFC 0005: one named event stream, three consumers
Events are noun.action, subscribed by name. Fossil has no such vocabulary — its hooks are artifact-level and its alerts are eight letters — so the delivery semantics come from its warning that a distributed system cannot promise exactly-once. (user: dmestas, size: 16429) [annotate] [blame] [check-ins using]
- Feature Name: `event-vocabulary` (one named event stream, three consumers) - Start Date: 2026-08-24 - Status: Draft for review - Depends on: RFC 0001 §4 (event bus), §5 (disposability), §6 (CI), §8 (OLTP) - Source authority: fossil `www/hooks.md` and `src/alerts.c` (both read from the mirror this forge serves), GitHub's webhook event reference, Gitea's webhook documentation, GitLab's project webhook events ## Summary [summary]: #summary quarry names the things that happen in a repository, once, in a vocabulary that pipelines, webhooks and notifications all subscribe to. An event is a **noun and an action** — `ticket.closed`, `landing.opened`, `branch.created` — carried on the bus that already exists, with a payload shape declared per noun. Today there are two and a half paths and no vocabulary. Webhooks derive an event's kind by slicing a notification's idempotency string. CI does not use events at all: it polls the index for new check-ins behind a per-repository watermark. Notifications have their own workflow names. Adding one more trigger — a landing opening, say — means either a third path or generalising anyway, so this RFC generalises first. The vocabulary is the load-bearing part, and the reason this is an RFC rather than a commit: a pipeline definition names events in its `on:` clause, so an event name is a **published interface**. Renaming one breaks every pipeline in every repository that used it, in a system where the pipeline definition is itself a versioned artifact in someone else's store. ## Motivation [motivation]: #motivation ### What exists `ci.Trigger` runs after every fold. It asks the index for check-ins newer than a watermark, reads `ci/*.json` at each one, registers the definition **at that check-in**, and starts a run. `pollCI` later polls unfinished runs and, on a terminal status, mints a `ci-pass` / `ci-fail` tag on the check-in. That is a complete, working pipeline trigger for exactly one event, with the event's identity left implicit. Four things in it are check-in-shaped: | | today | needed | |---|---|---| | trigger | poll `NewCheckins(watermark)` | subscribe to a named event | | payload | `{repo, checkin, branch, date, user, comment, cloneUrl, pipeline}` | per-noun, common envelope | | watermark | one check-in per repository | per subscription | | verdict sink | `WriteTag(verdict, checkin, runID)` | per-noun; a landing wants a reply | Every one of those blocks the landing trigger (quarry ticket `49323c33`), and none of them is made easier by doing the landing trigger first. ### What the field does Four vocabularies were read before proposing a fifth. **Fossil hooks** (`www/hooks.md`) are artifact-level and carry no semantics at all. Three types — `after-receive`, `before-commit`, `commit-msg` — and the after-receive hook's stdin is a list of artifact hashes with human-readable descriptions. There is no "on branch created" or "on merge". The doc states its purpose plainly: to "start up a background testing or CI process". **Fossil alerts** (`src/alerts.c`) carry fossil's only semantic vocabulary, as subscription letters on the `subscriber.ssub` column: a Announcements c Check-ins f Forum posts n New forum threads r Replies to my posts t Ticket changes u User permission changes w Wiki changes x Edits to forum posts Eight types. It splits the forum four ways by verb, and has no event for a branch, a tag, a technote or a merge. **GitHub** publishes 75 webhook events, most of which are not about version control: roughly six VCS core, fifteen collaboration, eight CI, ten security scanning, fifteen governance, and twenty platform and commerce events (marketplace, sponsorships, apps, Pages, Projects). quarry has a concept for about twenty of them. **Gitea** publishes about 27, **GitLab** 15. ### The shape decision The three forges disagree about the axis, and the disagreement is the design question: - **GitHub**: one event per noun, with an `action` field. `issues` fires for `opened`, `closed`, `labeled`, `assigned`, `edited`. - **Gitea**: one event per noun-verb pair. `issue_assign`, `issue_label`, `issue_milestone` and `issue_comment` are four separate events. - **GitLab**: coarse nouns, verbs folded into the payload. - **Fossil alerts**: mostly nouns, but `f`/`n`/`r`/`x` split the forum by verb. **quarry takes GitHub's.** Under Gitea's rule every new verb is a new permanent event name, and the name is a published interface. Under GitHub's, a subscriber can ask for `ticket` and get every change, or `ticket.closed` and get one, and adding a verb later costs nothing. Fossil's split shows the cost of the other choice inside one product: `f` and `n` and `x` are three names for three verbs on one noun, and a subscriber who wants "any forum activity" must name all three and remember to add the fourth when it appears. ## Guide-level explanation [guide-level-explanation]: #guide-level-explanation An event is `noun.action`. A subscriber names either the whole noun or one action of it: "on": ["checkin.created"] one action "on": ["ticket"] every action on the noun "on": ["landing.opened", "landing.reopened"] A pipeline with no `on:` clause runs on `checkin.created`, which is today's behaviour exactly, so every pipeline already in a repository keeps working without being edited. Every event carries the same envelope, and a payload keyed by its noun: ```json { "event": "landing.opened", "repo": "quarry", "at": "2026-08-24T09:48:57.123", "actor": "dmestas", "id": "activity:landing:9802c157…", "payload": { "landing": "9802c157…", "branch": "wiki-struct", "target": "trunk" } } ``` `id` is the idempotency key. It is stable for one occurrence of one event, and it is how a consumer that sees an event twice can tell that it has. ## Reference-level explanation [reference-level-explanation]: #reference-level-explanation ### §1 The vocabulary Nouns and their actions. An action marked † is not yet raised by any code path and is reserved so that adding it later is not a vocabulary change. | noun | actions | payload | |---|---|---| | `checkin` | `created` | hash, branch, parents, user, comment | | `branch` | `created`, `moved`, `closed`† | name, tip, previous tip | | `tag` | `created`, `removed`† | name, target, value | | `ticket` | `opened`, `changed`, `closed`, `reopened` | id, title, fields changed | | `wiki` | `edited`, `created`, `deleted` | title, hash | | `technote` | `created`, `edited` | event id, hash | | `forum` | `posted`, `replied`, `edited`†, `moderated` | thread root, post hash | | `landing` | `opened`, `commented`, `accepted`, `rejected` | id, branch, target | | `ci` | `started`, `completed` | run id, checkin or landing, verdict | | `mirror` | `pulled`, `failed` | url, artifacts received | | `repo` | `created`, `removed`, `settings` | name | | `account` | `added`, `caps`, `removed` | account, repository, caps | Fourteen nouns, thirty-odd actions. For comparison: fossil's alerts name eight things, GitHub's 75 events name about twenty that quarry has a concept for. Three of these exist in no other forge, and are here because quarry has the concept and an operator needs the hook: `technote` (fossil has the artifact but no alert for it), `mirror` (a forge that tracks 25 upstreams needs to fire on a failed pull), and `landing`. ### §2 Delivery semantics, which the medium decides Fossil's hook documentation states the constraint, and quarry inherits it rather than choosing it: > A push might not deliver all of the artifacts for a checkin. If Fossil knows > that a /xfer HTTP request is incomplete, it will defer running the > after-receive push for 60 seconds, or until a complete /xfer request is > received. This helps to prevent after-receive hooks from running when > incomplete checkins exist in the repository, **but it does not provide hard > guarantees, as there is no way to do that in a distributed system.** So: 1. **At-least-once.** A consumer may see an event twice. `id` is the idempotency key and a consumer that acts on an event MUST be idempotent under it. quarry's own notification plane already works this way. 2. **Possibly batched.** Fossil warns that two pushes' artifacts "might be combined into a single after-receive callback". quarry's fold has the same property; a single fold can produce many events, and a consumer must not assume one event per delivery. 3. **Possibly partial.** An event may describe state that is still arriving. A consumer that needs the whole picture reads the index at handling time rather than trusting the payload to be complete. 4. **Ordered within a repository, not across.** The bus preserves order per repository because the fold does; nothing orders two repositories against each other, and nothing should be written that needs it. ### §3 Handlers do not run inside the fold Fossil again: > Fossil holds a write transaction on the repository while the after-receive > hook is running. A hook that writes to the repository it was fired by therefore deadlocks. The same is true here for a different reason: quarry mints artifacts through the lease holder, and the fold is not it. **An event handler that mints an artifact runs outside the fold, through the lease holder, asynchronously.** The CI verdict already obeys this by accident of structure — `pollCI` runs on a timer, not in the ingest path. This RFC makes it a rule rather than an accident, because the landing verdict (`700b22b6`) would otherwise be written from exactly the wrong place. ### §4 One stream, three consumers | consumer | today | after | |---|---|---| | webhooks | `Raise()` from `fireNotify`, kind sliced out of a TxnID | subscribes by name | | CI | polls `NewCheckins` behind a watermark | subscribes by name | | notifications | own workflow names | subscribes by name | The watermark does not disappear: it becomes per-subscription rather than per-repository, because two consumers may be at different positions and one falling behind must not advance the other. ### §5 Verdict sinks A CI run's verdict is an artifact, because 0001 §6's no-hostage rule says the result must clone with the repository. Which artifact depends on the noun that triggered it: - `checkin.created` → a `ci-pass` / `ci-fail` **tag on the check-in**, as today. - `landing.opened` and `landing.commented` → a **reply in the landing's thread**. A landing is a forum thread; a verdict is commentary on a moment, a moving branch earns several, and tags do not accumulate. This is the shape quarry ticket `700b22b6` settled on and this RFC does not revisit it. The rule generalises: **the verdict takes the shape of the thing it judges.** ### §6 What is deliberately absent Named so the absence reads as a decision rather than an oversight: - **No security scanning events.** GitHub has ten. quarry scans nothing, and an event for a scan nobody runs is a promise to nobody. - **No package or registry events.** quarry hosts no packages. - **No marketplace, sponsorship, or app-installation events.** These are GitHub-the-product, not forge-the-idea. - **No `star` or `watch`.** quarry has subscriptions, which are a truthful signal about wanting to be told things; stars are a popularity one. - **No `fork`.** A zit clone is not an event in the origin: the origin does not learn of it, and an event it cannot honestly raise should not be named. - **No `before-*` events.** Every event here is a statement that something HAPPENED. A veto hook — fossil's `before-commit` — is a different mechanism with different failure modes (what does a forge do when a hook times out?), and mixing "tell me" with "may I" in one vocabulary is how both get harder. The last one is the one most likely to be asked for later. It should be its own RFC, and it should not reuse these names. ## Drawbacks [drawbacks]: #drawbacks **A published vocabulary is hard to change.** That is the point, and also the cost: a name chosen badly here is one every pipeline in every store repeats. The mitigation is the reserved actions in §1 and the noun-plus-action shape, which absorbs new verbs without new names. **One stream is a single point of failure** where today CI's polling is independently robust: if the bus stops, CI stops. The watermark survives, so nothing is lost, but a stalled bus becomes a stalled forge in a way a stalled poll loop is not. §2's at-least-once rule and per-subscription watermarks are what make recovery a replay rather than a repair. **Fourteen nouns is more than fossil has and fewer than GitHub.** Both comparisons will be made, and neither is the argument: the set is what quarry can honestly raise today plus what it will raise next. ## Rationale and alternatives [rationale-and-alternatives]: #rationale-and-alternatives **Do the landing trigger without a vocabulary.** Rejected: all four generalisations in the motivation table are needed for it anyway, and the result is a third trigger path. Ticket `49323c33` says so in its own words — "rides the existing event plane … rather than growing a second trigger path". **Adopt fossil's after-receive shape: hand the handler a list of artifacts.** Rejected. It is honest and it is what fossil does, but it pushes the whole interpretation problem to every consumer: each pipeline would re-derive "is this a new branch" from artifact hashes, and they would derive it differently. quarry already folds artifacts into meaning; the event stream should carry the meaning it already has. **Adopt Gitea's noun_verb naming.** Rejected in §Motivation: every new verb becomes a permanent name. **Use GitHub's names verbatim where they overlap.** Tempting for recognisability, and rejected in two places: `issues` is called `ticket` here because that is what fossil calls it and fossil compatibility is the north star, and `pull_request` is called `landing` because it is not one — nothing is transported and nobody requests a pull (zit#127). ## Prior art [prior-art]: #prior-art - **fossil** `www/hooks.md`: three hook types, artifact-level, no vocabulary. Its warning about distributed delivery is quoted in §2 and is the reason this RFC does not promise exactly-once. - **fossil** `src/alerts.c`: eight subscription letters, the only semantic event vocabulary fossil has. - **GitHub**: 75 events, noun-plus-action. The layering (VCS / collaboration / CI / security / governance / platform) is the useful part; most of the events are for products quarry does not have. - **Gitea**: ~27 events, noun_verb. - **GitLab**: 15 coarse events, verbs in the payload. ## Unresolved questions [unresolved-questions]: #unresolved-questions 1. **Does `branch.moved` fire per check-in or per fold?** A ten-commit push moves the branch once but creates ten check-ins. Firing per fold makes `branch.moved` cheap and coarse; firing per check-in makes it redundant with `checkin.created`. Leaning per fold, with the check-in count in the payload. 2. **Should `ci.completed` be subscribable?** It would let a pipeline trigger on another pipeline, which is either composition or a foot-gun. GitHub allows it (`workflow_run`) and guards against recursion. Deferred until something needs it. 3. **How does a subscription express "my repository only" versus fleet-wide?** The webhook plane is per-repository today; CI is per-repository; a fleet-wide subscriber (an operator watching `mirror.failed` across 25 stores) has no way to say so. 4. **JetStream delivery guarantees have not been traced.** §2 states what the vocabulary promises; whether the current bus configuration delivers it — durable consumers, redelivery, cursor persistence across restarts — is unverified and must be before CI moves off polling. ## Future possibilities [future-possibilities]: #future-possibilities - **Veto hooks** — fossil's `before-commit` and `commit-msg`, as their own RFC. - **Fleet-wide subscriptions**, resolving question 3. - **Event replay** — the bus retains the log, so "re-run every pipeline for the last hour" is a cursor rewind rather than new machinery. Attractive after an outage, and dangerous without §2's idempotency rule. - **`ci.completed` composition**, resolving question 2.