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.

packages/guard/repeat-tool-guard/src/index.ts

@@ -200,7 +200,10 @@ export function apply(ctx: Context, config: Config): void {
     const text = count === thresholds[0]
       ? GENTLE_REMINDER
       : detailedReminder(exec.name, count, previewArguments(canonical, argumentsPreviewChars))
-    return createUserMessage({ content: [{ type: 'text', text }], source: PLUGIN_SOURCE })
+    return createUserMessage({
+      content: [{ type: 'text', text }],
+      source: { ...PLUGIN_SOURCE, form: 'notice', summary: `${exec.name} × ${count}` },
+    })
   }
 
   // Observe-and-enrich, never veto: count first (state advances regardless of

packages/guard/repeat-tool-guard/tests/repeat-tool-guard.spec.ts

@@ -45,7 +45,14 @@ function reminders(agent: Agent): { text: string; source: unknown }[] {
     }))
 }
 
-const GUARD_SOURCE = { kind: 'plugin', plugin: 'repeat-tool-guard' }
+// The reminder is a `notice`-form context; its summary names the repeated
+// call so a reader sees it without expanding the row.
+const guardSource = (tool: string, count: number) => ({
+  kind: 'plugin',
+  plugin: 'repeat-tool-guard',
+  form: 'notice',
+  summary: `${tool} × ${count}`,
+})
 
 describe('threshold escalation', () => {
   it('reminds gently at the first default threshold (3) and in detail at the second (5)', async () => {
@@ -62,11 +69,11 @@ describe('threshold escalation', () => {
     const found = reminders(agent)
     expect(found).toHaveLength(2)
     expect(found[0]!.text).toContain('repeating the exact same tool call')
-    expect(found[0]!.source).toEqual(GUARD_SOURCE)
+    expect(found[0]!.source).toEqual(guardSource('probe', 3))
     expect(found[1]!.text).toContain('consecutive_calls: 5')
     expect(found[1]!.text).toContain('- tool: probe')
     expect(found[1]!.text).toContain('{"q":"same"}')
-    expect(found[1]!.source).toEqual(GUARD_SOURCE)
+    expect(found[1]!.source).toEqual(guardSource('probe', 5))
   })
 
   it('keys the gentle text to thresholds[0], not the literal 3', async () => {
@@ -327,7 +334,7 @@ describe('fold onto the downstream decision', () => {
     expect(found[0]!.text).toBe('downstream-ctx')
     expect(found[0]!.source).toEqual({ kind: 'plugin', plugin: 'test' })
     expect(found[1]!.text).toContain('repeating the exact same tool call')
-    expect(found[1]!.source).toEqual(GUARD_SOURCE)
+    expect(found[1]!.source).toEqual(guardSource('probe', 2))
     expect(found[2]).toEqual({ text: 'downstream-ctx', source: { kind: 'plugin', plugin: 'test' } })
     // The block's feedback reached the tool result unchanged.
     const results = [...agent.session.events].filter((e): e is SessionEvent<'tool/result'> => e.type === 'tool/result')