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.

packages/skill/tool-skill/src/index.ts

@@ -22,9 +22,37 @@ export const name = 'tool-skill'
 export const inject = ['agents', 'tools', 'skills']
 
 const DEFAULT_CATALOG_DESCRIPTION_MAX_LENGTH = 500
-const CATALOG_ENTRIES_START = '<available_skills>\n'
-const CATALOG_ENTRIES_END = '</available_skills>'
-const PLUGIN_SOURCE = { kind: 'plugin', plugin: 'dsh-tool-skill' } as const
+/**
+ * Durable provenance for one published session skill catalog. The catalog is a
+ * `catalog`-form context, so it records the entries it published beside the
+ * model-facing prose: a consumer presenting the list must not re-parse the
+ * `<available_skills>` block, whose framing exists for the model.
+ */
+export interface SkillCatalogSource {
+  readonly kind: 'skill-catalog'
+  readonly form: 'catalog'
+  /** Marks a replacement catalog rather than this session's first publication. */
+  readonly update?: true
+  /** Exactly the entries this message published, in catalog order. */
+  readonly entries: readonly { readonly name: string; readonly description: string }[]
+}
+
+declare module '@deepseek-ai/dsh-llm' {
+  interface MessageSourceMap {
+    'skill-catalog': SkillCatalogSource
+  }
+}
+
+/** Durable entry list mirroring the rendered catalog lines, for non-model consumers. */
+function catalogSourceEntries(
+  skills: SkillSummary[],
+  descriptionMaxLength: number,
+): SkillCatalogSource['entries'] {
+  return skills.map(skill => ({
+    name: skill.name,
+    description: catalogDescription(skill.description, descriptionMaxLength),
+  }))
+}
 
 /** Model-facing skill catalog configuration. */
 export interface Config {
@@ -142,13 +170,14 @@ export function apply(ctx: Context, config: Config = {}): void {
     signal.throwIfAborted()
     if (!snapshot.complete) return
     const skills = snapshot.skills.filter(isModelInvocable)
-    const digest = catalogDigest(skills, catalogDescriptionMaxLength)
+    const entries = catalogSourceEntries(skills, catalogDescriptionMaxLength)
+    const digest = digestCatalogEntries(entries)
     const history = catalogHistory(agent)
     if (history.visibleDigest === digest) return
     if (!history.published && skills.length === 0) return
     const catalog = history.published
-      ? renderCatalogUpdate(skills, catalogDescriptionMaxLength)
-      : renderCatalogMessage(skills, catalogDescriptionMaxLength)
+      ? renderCatalogUpdate(entries)
+      : renderCatalogMessage(entries)
     agent.inject(catalog)
   })
 }
@@ -199,8 +228,7 @@ function renderResourceHint(skill: Pick<SkillDefinition, 'provider' | 'resourceB
   }
 }
 
-function renderCatalogMessage(skills: SkillSummary[], descriptionMaxLength: number): UserMessage {
-  const entries = renderCatalogEntries(skills, descriptionMaxLength)
+function renderCatalogMessage(entries: SkillCatalogSource['entries']): UserMessage {
   return createUserMessage({
     content: [{
       type: 'text',
@@ -209,20 +237,23 @@ function renderCatalogMessage(skills: SkillSummary[], descriptionMaxLength: numb
         'A skill is a reusable set of task-specific instructions. The following skills are available in this session:',
         '',
         '<available_skills>',
-        ...entries,
+        ...renderCatalogEntries(entries),
         '</available_skills>',
         '',
         "If the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.",
         '</system-reminder>',
       ].join('\n'),
     }],
-    source: PLUGIN_SOURCE,
+    source: {
+      kind: 'skill-catalog',
+      form: 'catalog',
+      entries,
+    },
   })
 }
 
-function renderCatalogUpdate(skills: SkillSummary[], descriptionMaxLength: number): UserMessage {
-  const entries = renderCatalogEntries(skills, descriptionMaxLength)
-  const availability = skills.length === 0
+function renderCatalogUpdate(entries: SkillCatalogSource['entries']): UserMessage {
+  const availability = entries.length === 0
     ? [
       'No skills are currently available through the `skill` tool. Do not use names from earlier skill catalogs.',
     ]
@@ -237,28 +268,36 @@ function renderCatalogUpdate(skills: SkillSummary[], descriptionMaxLength: numbe
         'The available skill catalog changed. This complete catalog replaces every earlier available-skills list in this session:',
         '',
         '<available_skills>',
-        ...entries,
+        ...renderCatalogEntries(entries),
         '</available_skills>',
         '',
         ...availability,
         '</system-reminder>',
       ].join('\n'),
     }],
-    source: PLUGIN_SOURCE,
+    source: {
+      kind: 'skill-catalog',
+      form: 'catalog',
+      update: true,
+      entries,
+    },
   })
 }
 
-function renderCatalogEntries(skills: SkillSummary[], descriptionMaxLength: number): string[] {
-  return skills.map(skill => `- \`${skill.name}\`: ${catalogDescription(skill.description, descriptionMaxLength)}`)
+/** Model-facing catalog lines, projected from the same entries the source records. */
+function renderCatalogEntries(entries: SkillCatalogSource['entries']): string[] {
+  return entries.map(entry => `- \`${entry.name}\`: ${entry.description}`)
 }
 
-function catalogDigest(skills: SkillSummary[], descriptionMaxLength: number): string {
-  return digestCatalogEntries(renderCatalogEntries(skills, descriptionMaxLength).join('\n'))
-}
-
-function digestCatalogEntries(entries: string): string {
+/**
+ * Catalog identity over the durable entry list rather than the rendered prose.
+ * The entries are what changes; the surrounding `<system-reminder>` framing is
+ * written for the model and must not decide whether a republish is needed.
+ */
+function digestCatalogEntries(entries: SkillCatalogSource['entries']): string {
+  const canonical = entries.map(entry => `${entry.name}\u0000${entry.description}`).join('\n')
   return createHash('sha256')
-    .update(entries)
+    .update(canonical)
     .digest('hex')
 }
 
@@ -270,30 +309,14 @@ function catalogHistory(agent: Agent): { visibleDigest?: string; published: bool
     // The loop bounds prove the read-only event view contains this index.
     // oxlint-disable-next-line typescript/no-non-null-assertion
     const event = events[index]!
-    if (event.type !== 'user/message'
-      || event.data.source.kind !== 'plugin'
-      || event.data.source.plugin !== PLUGIN_SOURCE.plugin) continue
-    const digest = catalogContentDigest(event.data.content)
-    if (digest === undefined) continue
+    if (event.type !== 'user/message' || event.data.source.kind !== 'skill-catalog') continue
+    const digest = digestCatalogEntries(event.data.source.entries)
     published = true
     if (visible.has(event.seq)) return { visibleDigest: digest, published }
   }
   return { published }
 }
 
-function catalogContentDigest(content: UserMessage['content']): string | undefined {
-  if (content.length !== 1 || content[0]?.type !== 'text') return undefined
-  const text = content[0].text
-  const start = text.indexOf(CATALOG_ENTRIES_START)
-  if (start === -1) return undefined
-  const entriesStart = start + CATALOG_ENTRIES_START.length
-  const end = text.indexOf(CATALOG_ENTRIES_END, entriesStart)
-  if (end === -1) return undefined
-  const renderedEntries = text.slice(entriesStart, end)
-  const entries = renderedEntries.endsWith('\n') ? renderedEntries.slice(0, -1) : renderedEntries
-  return digestCatalogEntries(entries)
-}
-
 function catalogDescription(value: string, maxLength: number): string {
   const normalized = value.replaceAll(/\s+/g, ' ').trim()
   const truncated = normalized.length <= maxLength