[PerryLink]

Problem

Three walks run on a freshly parsed fence before validation/repair:

• normalizeGenuiSpec (src/client/genui-runtime/normalize.ts)
• defaultFileTreeDirectories, the file-tree type pass (same file)
• diagnoseUnknownGenuiFields (src/client/genui-runtime/diagnostics.ts)

All three recurse over the component tree with no depth bound. validateNode, repairNodeFields and walkTree do enforce GENUI_LIMITS.maxDepth = 8 / maxTreeDepth = 6, but they run after these walks, so a deeply nested fence overflows the stack before the spec can be rejected:

input	crash site
~1.1k-level / ~27 KB {"type":"col","items":[…]} chain	normalizeGenuiSpec
~2.5k-level file-tree children	defaultFileTreeDirectories
~2k-level nested tree	diagnoseUnknownGenuiFields

All three fail with RangeError: Maximum call stack size exceeded. Fence bodies are model output, so the input is untrusted and ~27 KB is not a large fence.

Fix

Thread the node depth through the three walks and stop at the same limits the rest of the pipeline already uses:

• root item = depth 0; depth 8 is accepted, depth 9 is the first rejected level (unchanged exceeds max depth 8 diagnostic);
• file-tree keeps maxTreeDepth + 1 = 7 levels, matching walkTree and the renderer's own depth > maxTreeDepth check (blocks/advanced.tsx);
• the over-deep subtree is returned as-is instead of walked. That is invisible to readers: validation rejects the fence and repair drops the tail anyway.

No renderer, schema or limit changes.

Tests

Four new tests in tests/genui-schema.spec.ts:

1. normalize normalizes exactly the rendered levels (alias at depth 8 works) and leaves depth 9 untouched; 4k-level input does not throw.
2. The full pipeline accepts depth 8 and rejects depth 9 with the usual diagnostic; 4k-level input does not throw.
3. Unknown-field diagnostics stop at maxDepth (reported at depth 8, not at depth 9).
4. The file-tree directory walk stops at maxTreeDepth; the deepest kept directory keeps its inferred dir marker.

On the base commit all four fail with RangeError; with the patch npx vitest run is 2110 passed / 152 files and npx tsc -p tsconfig.json --noEmit is clean. Specs within the documented depth limit are byte-identical before/after (26-spec equivalence set covering empty/single roots, every container, aliases, unknown fields and file-trees of 6/7/8 levels).