fix(pages): expose compile diagnostics through VFS

Author: Sg312

apps/sim/lib/copilot/vfs/workspace-vfs.ts

@@ -177,6 +177,11 @@ import { listAllWorkspaceFiles } from '@/lib/workspace-files/application/list-wo
 import { readWorkspaceFileContent } from '@/lib/workspace-files/application/read-workspace-file-content'
 import { listWorkspaceFileFoldersOperation } from '@/lib/workspace-files/application/workspace-file-folders'
 import { parseWorkspaceFileFolderDisplayPath } from '@/lib/workspace-files/folder-display-path'
+import {
+  collectSimPageDiagnostics,
+  isSimPageSource,
+  SIM_PAGE_CONTENT_TYPE,
+} from '@/lib/workspace-files/page-compile'
 import { getWorkspaceHostContextForViewer } from '@/lib/workspaces/host-context'
 import {
   assertActiveWorkspaceAccess,
@@ -1549,7 +1554,12 @@ export class WorkspaceVFS {
         const e2bFmt = isDocSandboxEnabled ? await getE2BDocFormat(record.name) : null
         const taskId = BINARY_DOC_TASKS[ext]
         const isMermaidFile = ext === 'mmd' || ext === 'mermaid'
-        if (!e2bFmt && !taskId && !isMermaidFile) return null
+        // Sim pages (and legacy .html-named page source) compile-check too:
+        // this is the only way an agent can retrieve the "block skipped"
+        // diagnostics for an ALREADY-written page — without it, "find the
+        // malformed table" degenerates into guessing.
+        const maybeSimPage = record.type === SIM_PAGE_CONTENT_TYPE || ext === 'html'
+        if (!e2bFmt && !taskId && !isMermaidFile && !maybeSimPage) return null
         const { content: buffer } = await readWorkspaceFileContent.execute({
           principal: this.requireFilePrincipal(),
           input: {
@@ -1565,6 +1575,37 @@ export class WorkspaceVFS {
             totalLines: 1,
           })
         }
+        if (maybeSimPage && isSimPageSource(code)) {
+          const diagnostics = collectSimPageDiagnostics(code)
+          const result =
+            diagnostics.length === 0
+              ? { ok: true }
+              : {
+                  ok: false,
+                  error: `${diagnostics.length} block(s) fail to compile and are omitted from the rendered page: ${diagnostics.join('; ')}`,
+                }
+          return bindWorkspaceFileResult(record, {
+            content: JSON.stringify(result),
+            totalLines: 1,
+          })
+        }
+        if (maybeSimPage && !e2bFmt && !taskId && !isMermaidFile) {
+          if (record.type === SIM_PAGE_CONTENT_TYPE) {
+            // A page-typed file whose bytes are not page source (e.g. a crash
+            // between upload registration and source restore) — report it
+            // rather than pretending the path does not exist.
+            return bindWorkspaceFileResult(record, {
+              content: JSON.stringify({
+                ok: false,
+                error:
+                  'Stored content is not page source (no YAML frontmatter with a title) — the file renders as raw HTML',
+              }),
+              totalLines: 1,
+            })
+          }
+          // Bespoke raw HTML has no compiler to check.
+          return null
+        }
         if (isMermaidFile) {
           const result = await validateMermaidSource(code)
           const json = JSON.stringify(result)

apps/sim/lib/workspace-files/page-compile.test.ts

@@ -106,18 +106,43 @@ describe('compileSimPage', () => {
     const source = '---\ntitle: T\n---\n```sim:kv\n- { key: }\n```'
     expect(compileSimPage(source)).not.toContain('was skipped')
     expect(collectSimPageDiagnostics(source)).toEqual([
-      'sim:kv block skipped: its payload did not match the expected shape',
+      'sim:kv block starting "- { key: }" skipped: its payload did not match the expected shape',
     ])
   })
 
   it('omits retired fence kinds and reports them as diagnostics', () => {
     const source = '---\ntitle: T\n---\n```sim:cards\n- title: X\n```'
     expect(compileSimPage(source)).not.toContain('sim:cards')
     expect(collectSimPageDiagnostics(source)).toEqual([
-      'sim:cards block skipped: its payload did not match the expected shape',
+      'sim:cards block starting "- title: X" skipped: its payload did not match the expected shape',
     ])
   })
 
+  // A page can carry several blocks of the same kind — the diagnostic must
+  // name WHICH one failed and distinguish a YAML syntax error from a shape
+  // mismatch, or "a table is malformed" sends the fixer hunting through all
+  // of them.
+  it('identifies the failing block by its first payload line and reports YAML errors', () => {
+    const source = [
+      '---',
+      'title: T',
+      '---',
+      '```sim:table',
+      'columns: [A, B]',
+      'rows:',
+      '  - [a, b]',
+      '```',
+      '',
+      '```sim:table',
+      'columns: [C: D]',
+      'rows: broken',
+      '```',
+    ].join('\n')
+    const diagnostics = collectSimPageDiagnostics(source)
+    expect(diagnostics).toHaveLength(1)
+    expect(diagnostics[0]).toContain('sim:table block starting "columns: [C: D]"')
+  })
+
   it('reports nothing for a fully valid page', () => {
     expect(
       collectSimPageDiagnostics('---\ntitle: T\n---\n```sim:kv\n- key: A\n  value: B\n```')

apps/sim/lib/workspace-files/page-compile.ts

@@ -1,3 +1,5 @@
+import { getErrorMessage } from '@sim/utils/errors'
+import { truncate } from '@sim/utils/string'
 import { JSON_SCHEMA, load } from 'js-yaml'
 import { marked } from 'marked'
 import { z } from 'zod'
@@ -407,20 +409,26 @@ function compileBody(source: string, diagnostics?: string[]): string {
         const renderer = FENCE_RENDERERS[kind]
         let payload: unknown
         let rendered: string | null = null
+        let parseError: string | null = null
         if (renderer) {
           try {
             payload = loadYaml(body)
-            rendered = renderer(payload)
-          } catch {
-            rendered = null
+          } catch (err) {
+            parseError = getErrorMessage(err, 'invalid YAML')
           }
+          if (parseError === null) rendered = renderer(payload)
         }
         if (rendered !== null) {
           html.push(rendered)
         } else {
-          diagnostics?.push(
-            `sim:${kind} block skipped: its payload did not match the expected shape`
-          )
+          // Name WHICH block failed and WHY: a page can carry several blocks
+          // of the same kind, and a bare "a table is malformed" sends the
+          // fixing agent hunting through all of them.
+          const preview = truncate(body.trim().split('\n')[0] ?? '', 80)
+          const reason = parseError
+            ? `its payload is not valid YAML/JSON — ${truncate(parseError, 160)}`
+            : 'its payload did not match the expected shape'
+          diagnostics?.push(`sim:${kind} block starting "${preview}" skipped: ${reason}`)
         }
       }
       index = bodyEnd + 1