fix(web): address the review round on the remaining context forms

- `relay` resolves its sender in `contextBody` like every other form. It was
  the one shape whose marker could claim a form the body did not render: an
  unreadable sender fell back inside the body while the row still said relay,
  contradicting the contract this PR's own note states.
- `recall` requires the retained, omitted, and truncated fields. Completeness
  is what the card exists to report, so a reference that cannot state it is
  not a readable recall — showing the label alone presents a confident card
  over unknown loss.
- The snapshot body states the supersession its producer framing line carries.
  That line is the one part of the model-facing text no section contains, and
  unlike an instruction context's `<system-reminder>` it states the form's own
  semantics rather than wrapping content.
- `GoalMessageSource` is a discriminated pair, so `{ form: 'notice' }` without
  its account no longer compiles. The guarantee this PR claims now holds at
  that seam too, not only through `ContextFormed` on plugin sources.
- Goal and tool-goal summaries are bounded by a shared `boundContextSummary`,
  which tool-tasks now uses as well. A goal objective is unbounded caller text
  in exactly the way a task label is.
- The runtime snapshot interpolates once per request: agent-loop renders the
  sections and joins them through `joinContextSections`.
- Every form's fallback branch is pinned, not only the notice one.

docs/core-data-structures/goal.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write docs/core-data-structures/goal.md
-goal.md: 8627b927fcff1c32faac0e76356f576bdbb29ba8
-goal.zh.md: f1c3a2e4d65d1efe849aab565e8beb79e0284aae
+goal.md: 5b9b751d734a98d5fc7b0333eeb52febadbca22a
+goal.zh.md: 0ce1a2166abc234225309bfb9a513bdf9ed30d4a

docs/core-data-structures/goal.md

@@ -101,22 +101,20 @@ Goal state changes use round `0`. A continuation consumer attributes each admitt
 
 ```ts type-equiv
 /** Message attribution for durable goal state and continuation rounds. */
-interface GoalMessageSource {
+type GoalMessageSource = {
   readonly kind: 'goal'
-  /**
-   * Round-zero state changes are `notice`-form contexts; a continuation round
-   * carries the objective forward as ordinary context and declares no form.
-   */
-  readonly form?: 'notice'
-  /** Present with `form`: one-line account of the mutation. */
-  readonly summary?: string
   readonly goalId: GoalId
   readonly revision: number
   /** Zero for state changes; positive for admitted continuation rounds. */
   readonly round: number
   /** Complete durable mutation carried only by round-zero state-change messages. */
   readonly change?: GoalChangeMeta
-}
+  /**
+   * Round-zero state changes are `notice`-form contexts; a continuation round
+   * carries the objective forward as ordinary context and declares no form.
+   * Discriminated so the account cannot be omitted when the form is declared.
+   */
+} & ({ readonly form: 'notice'; readonly summary: string } | { readonly form?: never; readonly summary?: never })
 ```
 
 ## Requests and notifications

docs/core-data-structures/goal.zh.md

@@ -101,22 +101,20 @@ interface GoalClearChangeMeta {
 
 ```ts type-equiv
 /** Message attribution for durable goal state and continuation rounds. */
-interface GoalMessageSource {
+type GoalMessageSource = {
   readonly kind: 'goal'
-  /**
-   * Round-zero state changes are `notice`-form contexts; a continuation round
-   * carries the objective forward as ordinary context and declares no form.
-   */
-  readonly form?: 'notice'
-  /** Present with `form`: one-line account of the mutation. */
-  readonly summary?: string
   readonly goalId: GoalId
   readonly revision: number
   /** Zero for state changes; positive for admitted continuation rounds. */
   readonly round: number
   /** Complete durable mutation carried only by round-zero state-change messages. */
   readonly change?: GoalChangeMeta
-}
+  /**
+   * Round-zero state changes are `notice`-form contexts; a continuation round
+   * carries the objective forward as ordinary context and declares no form.
+   * Discriminated so the account cannot be omitted when the form is declared.
+   */
+} & ({ readonly form: 'notice'; readonly summary: string } | { readonly form?: never; readonly summary?: never })
 ```
 
 ## 请求与通知