feat(web): declare the remaining context forms on every shipped producer

Four values complete the vocabulary, so the opaque body is reached only by
producers that genuinely promise no shape.

`snapshot` — current state a later snapshot supersedes. system-prompt now
exposes `renderContextSections()`, the named contributions
`renderContextSnapshot()` already joins for the model, so the body attributes
each part to the subsystem that produced it instead of re-splitting joined
prose. The runtime snapshot, time-context, and tmux-context declare it.

`notice` — a one-off account of what just happened, declared by tool-tasks,
goal state changes, tool-goal wrap-up, plan-mode switches, and
repeat-tool-guard. Its `summary` rides the COLLAPSED row: these five are the
majority of shipped producers and none of them needs expanding to be read.
The task summary bounds itself because its inputs are unbounded caller text.

`relay` — a message another agent addressed to this one; both subagent
sources declare it and the body names the sender above what it said.

`recall` — material lifted from another session's log. session-reference
needed no new field: its references already record retained and omitted
counts and the truncation flag, which the body shows first, because recalled
context is bounded on the way in.

`ContextFormed` is now discriminated by `form`, so a producer cannot declare
a shape without the facts that shape is presented from — a notice without its
summary, or a snapshot without its sections, fails to compile.

Only the two hook bridges stay opaque, by design: their content is whatever
an external program printed, so no shape can be promised for it. Unknown
kinds and unreadable records land there too.

.agents/notes/implemented/feature/2026-08-05-context-form-vocabulary.md

@@ -29,6 +29,14 @@ Entries record the published fact **unescaped**. The pseudo-XML escaping belongs
 
 That move also relocates catalog **identity**: the republish digest now covers the durable entries rather than the rendered text, so the model-facing framing can no longer decide whether a republish is needed, and the text-slicing that recovered entries from a logged message is gone. A resumed session whose newest catalog predates this change republishes once, which the pre-release stance permits. One case does not self-heal: if that old-format catalog is the only one and the current view has no skills, the plugin sees no published catalog and emits no tombstone, so the model keeps a stale catalog nothing replaces. The pre-release stance ("backends reject old on-disk formats") permits it; it is recorded here rather than left to the optimistic path.
 
+**`snapshot`** — current state that a later snapshot from the same producer supersedes. The runtime-context snapshot, `time-context`, and `tmux-context` declare it. `renderContextSections()` exposes the assembly's named contributions, which `renderContextSnapshot()` already joined for the model, so the body attributes each part to the subsystem that produced it without re-splitting joined prose. The two single-contribution producers record one section each. The cleared runtime-context marker has no contributions left and declares no form.
+
+**`notice`** — a one-off account of something that just happened. `tool-tasks`, `goal` state changes, `tool-goal` wrap-up, `plan-mode` switches, and `repeat-tool-guard` reminders declare it with a `summary`, which rides the **collapsed** row: a notice is meant to be read without expanding at all. The summary is bounded where its inputs are caller text (a task's label and status detail have no length of their own).
+
+**`relay`** — a message another agent addressed to this one. Both subagent-addressed sources declare it; the sender is shown as the opaque session id the source already records, because this client cannot resolve it to a title.
+
+**`recall`** — material lifted out of another session's log. `session-reference` declares it and needed no new field: its references already record the label, retained and omitted counts, and truncation flag, which the body shows first, because recalled context is bounded on the way in and a card that hid the omitted count would overstate what the model received.
+
 Both readers are **all-or-nothing**: one unreadable entry disqualifies the record rather than being dropped, because a body that replaces the model-facing text must not present a confident but incomplete account of what the model read. The row's form marker reports what actually rendered, not what was declared.
 
 The producer side validates the same durable data with the same posture. `catalogHistory` reads `source.entries` out of `agent.session.events`, which on resume or fork is a JSONL/SQLite seed whose validation only guarantees a source object with a non-empty `kind` — no per-kind field is checked. An unreadable catalog is therefore skipped as "not this plugin's record", the posture the replaced content digest had; throwing there would fail every later step of that session at the latest, least diagnosable point.
@@ -61,4 +69,5 @@ The tool seam pairs its vocabulary with `presentCall(args)`, a host-side pure fu
 - A reader can tell what was added without expanding, and reading it no longer means reading escaped JSON.
 - The durable `MessageSource` now carries a semantic classification beside provenance. The boundary is load-bearing: facts and shape only, never presentation. A producer that wants a better card records better facts.
 - Catalog identity no longer depends on the model-facing prose, deleting the text-slicing path that could mistake a reworded catalog for a changed one.
-- Five forms from the surveyed taxonomy (`snapshot`, `relay`, `recall`, `notice`, and the unclassified remainder) are not declared yet; their producers render opaque until they record the fields their form needs.
+- Every shipped producer except the two hook bridges now declares a form. The bridges stay opaque by design: their content is whatever an external program printed, so no shape can be promised for it. Unknown kinds and unreadable records land there too.
+- `ContextFormed` is discriminated by `form`, so a producer cannot declare a shape without the facts that shape is presented from — a `notice` without its summary, or a `snapshot` without its sections, fails to compile.