chore: consolidate chat.agent / Sessions / Skills changesets (26 → 8)

Roll up all the chat.agent feature work that's been accumulating on this
branch into 8 user-facing CHANGELOG entries. No behavior change — just
tidying up the .changeset/ directory before merge.

Final shape:

- chat-agent.md (sdk minor + core patch) — the headline; folds 13:
  ai-sdk-chat-transport, ai-chat-sandbox-and-ctx, chat-agent-*,
  chat-customagent-session-binding-and-stop-fixes,
  chat-reconnect-isstreaming-optional, chat-run-pat-renewal,
  chat-store-primitive, chat-transport-session-renew-plus-preload,
  drop-legacy-chat-stream-constants, dry-sloths-divide,
  trigger-chat-transport-watch-mode.
- sessions-primitive.md (core + sdk patch) — folds 3: session-primitive,
  session-sdk-toolkit, session-trigger-config-extra-fields.
- agent-skills.md (sdk + core + build + cli patch) — folds 2:
  chat-agent-skills-phase-1, skills-runtime-subpath.
- ai-tool-helpers.md (sdk patch) — folds 2: ai-tool-execute-helper,
  ai-tool-toolset-typing.
- mock-chat-agent-test-harness.md (sdk + core patch) — folds 3:
  mock-chat-agent-test-harness, mock-task-context-test-infra,
  mock-chat-agent-setup-locals.
- mcp-agent-chat-sessions.md (cli patch) — kept standalone.
- add-is-replay-context.md (core patch) — kept standalone (general task feature).
- truncate-error-stacks.md (core patch) — kept standalone (general infra).

Bumps preserved (chat-agent stays minor on sdk; everything else patch).
Auto-named "dry-sloths-divide" got merged into chat-agent and dropped.

Author: ericallam

.changeset/agent-skills.md

@@ -0,0 +1,18 @@
+---
+"@trigger.dev/sdk": patch
+"@trigger.dev/core": patch
+"@trigger.dev/build": patch
+"trigger.dev": patch
+---
+
+Agent Skills — developer-authored folders (`SKILL.md` + scripts/references/assets) bundled into the deploy image automatically and discovered by the chat agent via progressive disclosure. Built on the [AI SDK cookbook pattern](https://ai-sdk.dev/cookbook/guides/agent-skills) — portable across providers.
+
+**SDK:**
+
+- `skills.define({ id, path })` registers a skill with the resource catalog; the Trigger.dev CLI bundles the folder into `/app/.trigger/skills/{id}/` automatically — no `trigger.config.ts` changes, no build extension.
+- `SkillHandle.local()` reads the bundled `SKILL.md` at runtime, parses frontmatter, returns a `ResolvedSkill`.
+- `chat.skills.set([...])` stores resolved skills for the current run.
+- `chat.toStreamTextOptions()` auto-injects the skills preamble into the system prompt and merges three tools — `loadSkill`, `readFile`, `bash` — scoped per-skill with path-traversal guards and output caps (64 KB stdout/stderr, 1 MB `readFile`). `bash` runs with `cwd` = skill directory; the turn's abort signal propagates.
+- `@trigger.dev/sdk/ai/skills-runtime` subpath — the `bash` + `readFile` runtime primitives (backed by `node:child_process` + `node:fs/promises`) live here, not in `@trigger.dev/sdk/ai`. Fixes client-bundle build errors (`UnhandledSchemeError: Reading from "node:child_process"…`) that hit Next.js + Webpack when a browser page imports types from `@trigger.dev/sdk/ai` (for example `ChatUiMessage` via a shared tools file). The chat-agent factory loads the runtime lazily via a computed-string dynamic import, so server workers still get full skill support without any caller changes.
+
+This is the SDK + CLI layer only — no backend, no dashboard overrides yet. Dashboard-editable `SKILL.md` text and override flow are on the roadmap; `skill.resolve()` currently throws.

.changeset/ai-chat-sandbox-and-ctx.md

@@ -0,0 +1,8 @@
+---
+"@trigger.dev/sdk": patch
+---
+
+AI SDK `tool()` helpers for Trigger subtasks:
+
+- `ai.toolExecute(task)` — pass Trigger's subtask/metadata wiring as the `execute` handler to AI SDK `tool()` while you define `description` and `inputSchema` yourself. `ai.tool()` is now refactored to share the same internal handler.
+- `ai.tool(task)` (`toolFromTask`) aligns with AI SDK `ToolSet`: Zod-backed tasks use static `tool()`; returns are asserted as `Tool & ToolSet[string]`. Minimum `ai` devDependency raised to `^6.0.116` so emitted types resolve the same `ToolSet` as apps on AI SDK 6.0.x — avoids cross-version `ToolSet` mismatches in monorepos.