refactor(canvas): move freeform authoring contract to @posthog/shared

Relocate the freeform canvas authoring contract — the system-prompt builder
(freeformSystemPromptFor), the import whitelist, the starter scaffold, and the
freeform template id — from @posthog/core into @posthog/shared, so @posthog/agent
can consume it (for the canvas_checkout tool) without a core↔agent package cycle.

Pure move: @posthog/core/canvas/{canvasTemplates,freeformSchemas,freeformWhitelist,
freeformStarter} now re-export from @posthog/shared, so existing consumers are
unchanged.

Generated-By: PostHog Code
Task-Id: 2ed89933-091b-446c-af91-5cc72d939b3b

Author: adboio

packages/core/src/canvas/canvasTemplates.ts

@@ -1,9 +1,6 @@
+import { freeformSystemPromptFor } from "@posthog/shared/canvas-freeform-prompt";
 import { injectable } from "inversify";
-import {
-  BUILT_IN_TEMPLATES,
-  type CanvasTemplate,
-  freeformSystemPromptFor,
-} from "./canvasTemplates";
+import { BUILT_IN_TEMPLATES, type CanvasTemplate } from "./canvasTemplates";
 import type { ICanvasTemplatesService } from "./services";
 import type { CanvasTemplateSummary } from "./templateSchemas";
 

packages/core/src/canvas/canvasTemplatesService.ts

@@ -1,5 +1,6 @@
 import type { AuthService } from "@posthog/core/auth/auth";
 import { AUTH_SERVICE } from "@posthog/core/auth/auth.module";
+import { FREEFORM_TEMPLATE_ID } from "@posthog/shared/canvas-freeform-prompt";
 import { inject, injectable } from "inversify";
 import type {
   DashboardFileMeta,
@@ -11,7 +12,7 @@ import {
   type DesktopFsClient,
   type FsEntryBase,
 } from "./desktopFsClient";
-import { FREEFORM_TEMPLATE_ID, type FreeformVersion } from "./freeformSchemas";
+import type { FreeformVersion } from "./freeformSchemas";
 import { fetchCurrentUser } from "./posthogApi";
 
 // Desktop file-system "type" tag for a dashboard entry. Channels are `folder`

packages/core/src/canvas/dashboardsService.ts

@@ -2,10 +2,10 @@ import { z } from "zod";
 
 // The template id for freeform-React canvases. Stored on a canvas's meta so the
 // generation path can resolve the right system prompt.
-export const FREEFORM_TEMPLATE_ID = "freeform";
 
 // A single point in a freeform canvas's edit history. Every agent turn appends
-// one full-file snapshot (Q7: full-file rewrite); the user can revert to any of
+// one full-file snapshot (the agent edits a local scratch copy incrementally,
+// then publishes the finished file wholesale); the user can revert to any of
 // them and the `currentVersionId` pointer is what publishes. We keep whole-file
 // snapshots rather than diffs because canvases are small and a snapshot can
 // never fail to reconstruct.

packages/core/src/canvas/freeformSchemas.ts

@@ -8,6 +8,18 @@
       "types": "./dist/index.d.ts",
       "import": "./dist/index.js"
     },
+    "./canvas-freeform-prompt": {
+      "types": "./dist/canvas-freeform-prompt.d.ts",
+      "import": "./dist/canvas-freeform-prompt.js"
+    },
+    "./canvas-freeform-whitelist": {
+      "types": "./dist/canvas-freeform-whitelist.d.ts",
+      "import": "./dist/canvas-freeform-whitelist.js"
+    },
+    "./canvas-freeform-starter": {
+      "types": "./dist/canvas-freeform-starter.d.ts",
+      "import": "./dist/canvas-freeform-starter.js"
+    },
     "./analytics-events": {
       "types": "./dist/analytics-events.d.ts",
       "import": "./dist/analytics-events.js"

packages/shared/package.json

@@ -3,7 +3,7 @@ import {
   buildImportMap,
   checkFreeformImports,
   FREEFORM_WHITELIST,
-} from "./freeformWhitelist";
+} from "./canvas-freeform-whitelist";
 
 describe("checkFreeformImports", () => {
   it("accepts whitelisted imports", () => {

packages/shared/src/canvas-freeform-prompt.ts

@@ -5,6 +5,9 @@ export default defineConfig({
     "src/index.ts",
     "src/agent-platform-types.ts",
     "src/analytics-events.ts",
+    "src/canvas-freeform-prompt.ts",
+    "src/canvas-freeform-starter.ts",
+    "src/canvas-freeform-whitelist.ts",
     "src/constants.ts",
     "src/deeplink.ts",
     "src/dismissalReasons.ts",