fix(graph): classify multi-assigned instance field as field-reassign, not uid-collision

[coseto6125]

Problem

An instance field assigned in more than one place — self.x = … in __init__ then again in another method (Python), this.x = … (JS/TS), @x = … (Ruby), a Rust struct field re-set, etc. — emits two RawNodes with identical (kind=Property, path, owner, name), i.e. a uid collision. The second is correctly deduped to one node.

But this is the most common OO idiom, not a parser bug. It was classified as uid-collision ("true parser ambiguity worth investigating") and recorded a BlindSpot, which made ecp inspect / ecp impact report traversal may be incomplete for ordinary code — a false "no data" signal that misleads the consuming LLM.

Found via dogfooding

On a real repo, ecp inspect --name warmup_bot reported:

uid-collision: first=Property…CacheManager_refresh_task second=Property…CacheManager_refresh_task
note: traversal may be incomplete

_refresh_task is a single field set in __init__ (line 89) and reassigned in warmup_bot (line 235). Nothing is ambiguous; the graph has exactly one node for it. The BlindSpot was pure noise that flagged the traversal as unreliable.

Fix

classify_collision (the shared collision classifier in resolution/builder.rs) now returns field-reassign for a non-C-family Property self-collision, and the build dedup path records no BlindSpot for that kind — the dedup loses no information (both nodes ARE the same field). The tombstone still runs, so node-position alignment is unchanged.

Untouched: real collisions still report uid-collision (Variable/Impl/Class duplicates), C-family Property stays ifdef-redef (header redefinition, not an OO field), method overloads stay method-overload.

Why not "add line to the uid"

Including the assignment line in the uid would split one field into N distinct nodes — scattering its references across duplicates and making ecp impact less complete, not more. The uid (kind, path, owner, name) correctly expresses "one class's one field = one identity"; the bug was in how the resulting self-collision was classified, not in the identity.

Tests

• New field_reassign_not_collision.rs: reassigned field dedups to one node, emits no uid-collision BlindSpot, and a non-field duplicate Variable still reports uid-collision (guards against over-suppression).
• Unit classify_non_c_property_is_field_reassign (py/js/Rust → field-reassign; C-family → ifdef-redef); updated the existing fall-through test (its old assumption that Property falls through to uid-collision was the bug).
• Full ecp-analyzer suite green.
• E2E: re-indexed a real repo; warmup_bot no longer emits the collision BlindSpot and get_for_search impact no longer flags traversal-incomplete.

Language-neutral: the fix is in the shared classifier, covering every OO language's field-reassignment at once — the 14-language dimension is satisfied at the classification layer rather than per-parser.

[github-actions]

ecp impact cache (0 symbols) — internal, used by ecp dev pr-analyze

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