Remove deprecated Eagle3 legacy model from converter

[guan404ming]

Purpose

Part of the legacy code removal item in #781.

• Delete deprecated eagle3_legacy_model.py; its forward() was never implemented and it only served as a weight skeleton for the Eagle3 converter.
• Convert with the training-side Eagle3DraftModel instead, following the DFlash converter pattern. Net -387 lines.
• Side fix: the legacy skeleton hardcoded a single decoder layer, silently dropping layers.1.* weights of multi-layer checkpoints. Eagle3DraftModel builds all layers, so they are now preserved.

Tests

• New unit test in test_eagle3_converter.py: converts a tiny 2-layer checkpoint and asserts the saved state dict keeps every decoder layer, contains only source-checkpoint keys, and round-trips values exactly.
• tests/unit/convert/: 52 passed. make quality (ruff + mypy) passes.

Checklist

I have filled in:

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan/results, such as providing test command and pasting the results.
• (Optional) The necessary documentation update.
• I (a human) have written or reviewed the code in this pr to the best of my ability.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 1afb3b2 and fce748e.

📒 Files selected for processing (4)

• src/speculators/convert/eagle/eagle3_converter.py
• src/speculators/convert/eagle/eagle3_legacy_model.py
• tests/integration/convert/test_eagle3.py
• tests/unit/convert/test_eagle3_converter.py

💤 Files with no reviewable changes (1)

• src/speculators/convert/eagle/eagle3_legacy_model.py

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📝 Walkthrough

Walkthrough

Changes

The EAGLE-3 conversion flow now creates and validates Eagle3DraftModel checkpoints. It filters verifier-filled missing keys, saves only remapped input weights, removes the legacy speculator implementation, and updates unit and integration tests.

EAGLE-3 draft conversion

Layer / File(s)	Summary
Converter model and call-path migration src/speculators/convert/eagle/eagle3_converter.py	The converter uses Eagle3DraftModel, derives target vocabulary size from t2d, filters verifier-filled keys, and simplifies save/validation method signatures.
Checkpoint filtering and validation src/speculators/convert/eagle/eagle3_converter.py, tests/unit/convert/test_eagle3_converter.py	Checkpoint saving retains remapped input weights, validation checks selected tensors for NaNs, and unit coverage verifies layer preservation and exact tensor values.
Legacy model and integration updates src/speculators/convert/eagle/eagle3_legacy_model.py, tests/integration/convert/test_eagle3.py	The legacy Eagle3Speculator implementation and forward-pass helper are removed, while integration tests load converted checkpoints as Eagle3DraftModel instances.

Possibly related PRs

• vllm-project/speculators#670: Adds Eagle3DraftModel and Eagle3SpeculatorConfig behavior that intersects with this converter’s draft-model checkpoint flow.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: removing the deprecated Eagle3 legacy model from the converter.
Description check	✅ Passed	The description matches the PR scope by explaining the legacy model removal, the draft-model switch, and the added tests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[speculatorsbot]

LGTM. Clean removal of the deprecated legacy model, correctly replaces it with Eagle3DraftModel following the DFlash converter pattern. The side fix for multi-layer checkpoint preservation is correct and well-tested. Recommend approving.

🤖 Generated with Claude Code using the /pr-review skill

[mergify]

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