feat(web): split context injection into producer-declared forms

Injected context reached the transcript as one anonymous shape whose
expanded body was the whole message serialized as inline JSON, so the
escaping collapsed the only readable part — the model-facing prose —
into a single line.

`MessageSource` gains an optional producer-declared `form`, a small
semantic vocabulary of information shapes independent of `kind`: kind
says who produced the context, form says what shape it is, so several
producers may share one presentation. Two values ship.

`instructions` (workspace-context) lists the reconciled files above
their text and keeps the `<system-reminder>` framing verbatim, because
the framing is part of what the model read. `catalog` moves dsh-tool-skill
off the shared plugin kind onto a `skill-catalog` source carrying the
published name/description entries, and the body lists those instead of
re-parsing `<available_skills>` out of the prose. Catalog identity moves
with it: the republish digest now covers the durable entries, deleting
the text-slicing that recovered them from a logged message.

Everything else renders the opaque body — the model-facing text with its
real line breaks, then the remaining provenance as fields. That is the
documented default, not a leftover: a resumed, forked, or foreign log
must render whether or not its producer is mounted here, which is why
the classification lives in the durable source rather than a client-side
table keyed by producer.

docs/config-catalog.md

@@ -1916,7 +1916,7 @@ export interface Config {
 }
 ```
 
-Source: [`packages/skill/tool-skill/src/index.ts:30`](../packages/skill/tool-skill/src/index.ts)
+Source: [`packages/skill/tool-skill/src/index.ts:58`](../packages/skill/tool-skill/src/index.ts)
 
 ## `@deepseek-ai/dsh-tool-str-replace-editor`
 

docs/core-data-structures/core.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/core.md
-core.md: 1b5704384157688b45ae0900bf2d9924426bbd6b
-core.zh.md: 05802039920163ac8185703ab483c5603087ed96
+core.md: 6c12b8af07498590bb8eb5b92c3c8f6bbef313f3
+core.zh.md: f83e8873adfae5ab81c02678605f4014214b96b6

docs/core-data-structures/core.md

@@ -161,7 +161,7 @@ Where a message came from is itself a merge-extensible sum type:
  */
 interface MessageSourceMap {
   user: { kind: 'user' }
-  plugin: { kind: 'plugin'; plugin: string }
+  plugin: { kind: 'plugin'; plugin: string } & ContextFormed
   model: ModelMessageSource
   tool: ToolMessageSource
 }

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

@@ -167,7 +167,7 @@ interface Message {
  */
 interface MessageSourceMap {
   user: { kind: 'user' }
-  plugin: { kind: 'plugin'; plugin: string }
+  plugin: { kind: 'plugin'; plugin: string } & ContextFormed
   model: ModelMessageSource
   tool: ToolMessageSource
 }