D284 — hook.json is validated against one declared event vocabulary, on write, at sync and in lint

Decision. hookEventReach (internal/provisioning/hookspec.go) is the single table of the canonical hook events, each with the providers that fire it. ValidateHookJSON reads it: artifact_write refuses a hook.json that is not valid JSON, lacks event or command, or has a relative command climbing out of the hook's directory, and accepts an event outside the table with a warning; lint reports the same hooks already in a KB (hook_invalid, warning). At sync, every registrar turns a hook.json it cannot use into an AppliedResult.Warnings entry naming the hook and the reason, and the claude and codex registrars consult the table too: an event the client does not fire (PreInvocation) is not registered, an event outside the table is registered as declared but warned about.

Why. A broken hook was invisible from authoring to sync: the files were materialized and counted (hook 1/1) and nothing ever fired. Reject-at-write is the only point where the author can still fix it cheaply; the warning at sync and the lint check cover what arrives by git or was written before. Sync stays tolerant (it never fails Apply and still registers an unknown event) because a KB may be newer than the client, but it is no longer silent.

Alternatives rejected. - Reject unknown events only at write and keep sync silent: leaves a hook that arrives by git broken with no signal. - Reject unknown events at write: the table holds only the events this repository encodes, so a real client event it lacks would become unwritable; a warning catches the typo without that cost. - Make sync refuse an unknown event: a KB carrying an event this client's table predates would lose a hook that works on the real client. - Fold openCodeHookEvents and antigravityHookEvents into the table: they carry the client mapping, not a yes/no; a test pins that the two agree with the table instead. - Reject an event that some connected client will not fire: a hook may deliberately target one client. The write result lists the clients that will not fire it instead. - Guess the events of a client that the repo does not already encode (e.g. Claude Code events beyond the ones here): out of scope; adding one is a line in the table.

Consequences. The vocabulary is only as wide as the events the repository already encodes for a client (SessionStart, UserPromptSubmit, PreToolUse, PostToolUse, Stop, SubagentStop, PreCompact, PreInvocation, PostInvocation); a legitimate client event missing from it (Claude Code's Notification, for one) is accepted with a warning on write, and by lint, until it is added to the table (and to the registrar's mapping if that client needs one). Adding a provider's mapping means updating both the table and that provider's map. A hook.json missing from a hook directory is now also a sync warning.