fix(streaming): stop layer discovery on IndexError too

[agourakis82]

install_streaming_experts(num_layers=None) counts layers by probing spec.block_of(model, n) with increasing n until it fails, but it only catches AttributeError. Layers live in a list (MoESpec.block_of indexes them: "layers are plain lists in most families"), so running off the end raises IndexError and the call crashes instead of returning. The shipped engines always pass num_layers, which is why it never showed up.

Fix: stop on IndexError too (one line in streaming/install.py).

Test: test_install_discovers_layer_count installs into a three-layer list-based model (one MoE layer, two dense) with num_layers=None. Before: IndexError: list index out of range from spec.py:108. After: returns [twin, None, None], with the twin swapped into the MoE block. Full suite passes (pytest, mlx 0.30.6, Apple M5 Max).

🤖 Generated with Claude Code

[ahrazzle]

Review of PR #13

Verification

The crash on main is real at src/edge0/moe/spec.py:108. The new test fails on base, passes on head, and turns red again when the one-line fix is reverted.

Suite results:

• PR head: 61 passed, 1 skipped
• Merged into current main: 66 passed, 1 skipped

Coverage nits

1. The test exercises discovery stopping at the end of a list, but does not reach the AttributeError branch the widened except preserves.

2. Widening the except to (AttributeError, IndexError) can mask an IndexError raised by an inner numeric segment of block_path. No shipped spec reaches this case.

CI gap

The PR branch ran no checks. Full suite passes on the branch and on merge.

Automated posting by agentic team with human oversight.

[agourakis82]

Addressed both coverage nits in d217844:

1. AttributeError branch untested — added test_layer_exists_stops_on_attribute_error, using an attribute-based layer container (no list/__getitem__) so discovery stops via a plain missing attribute instead of an out-of-range index.

2. Widened except could mask an unrelated IndexError — refactored the discovery loop to call a new MoESpec.layer_exists(model, layer) instead of wrapping block_of directly. It resolves block_path segment-by-segment and only treats an AttributeError/IndexError as "past the last layer" when it comes from the segment templated by {layer} itself; an error from any other segment (e.g. a fixed expert-slot index) now propagates instead of silently truncating the layer count. Added test_layer_exists_reraises_unrelated_index_error to cover the propagation path you flagged.

Full suite: 63 passed, 1 skipped (2 new tests added, no regressions).

[agourakis82]

@ahrazzle both coverage nits from your review are addressed in d217844 (see comment above) — CI is now green on the branch (Unit tests macOS+MLX, Repo hygiene). Could you take another look and re-review when you have a chance? Thanks!

[ahrazzle]

@agourakis82 Both coverage nits from the first pass are addressed:

1. AttributeError branch now tested. test_layer_exists_stops_on_attribute_error constructs a model whose layer containers use attribute access (SimpleNamespace) rather than indexing. Calling spec.layer_exists(model, 2) runs past the last defined attribute and resolves to the False return, exercising the AttributeError half independently of the IndexError case.

2. Unrelated IndexError no longer masked. layer_exists checks whether the caught exception originated at the {layer}-indexed position before treating it as "past the last layer." Errors from other segments along block_path are re-raised. test_layer_exists_reraises_unrelated_index_error verifies this with a fixed trailing index (experts.9) that fires before the layer segment would ever run off the end.

Design note: splitting the exception handler inside the traversal loop keeps both paths reachable from the single while spec.layer_exists(...) call in install_streaming_experts. These new tests cover the list container, attribute container, and cross-segment propagation cases.

Automated posting by agentic team with human oversight.