feat(elixir): index Elixir with Phoenix, Plug and Ecto flow coverage

[ferrine]

Elixir's grammar has no declaration node types — defmodule, def, alias, an Ecto schema and a Phoenix route are all the same call node, told apart only by the text of the target identifier. So the generic node-type ladder has nothing to match and every construct is dispatched through the visitNode hook, which also owns call extraction (visitFunctionBody does not invoke the hook, and Elixir call sites live inside bodies).

Three things beyond plain symbol extraction:

• Alias expansion — alias Foo.{A, B}, as:, __MODULE__ and the implicit nested-module alias — so a call written Repo.insert(...) carries MyApp.Repo::insert and resolves by exact qualified name instead of by bare name.
• Clause merging by (module, name, arity). The GenServer idiom spells a multi-clause function as repeated defs, which otherwise index as one identical node per clause and scatter every caller edge.
• Macro-argument dispatch, closed end to end rather than half-bridged: Phoenix routes become route nodes linked to the controller action they dispatch to (nested scope path + alias composition, resources expansion, forward, live); plug :atom / plug Module link to the function or call/2 that runs; Ecto schema fields and association target modules are extracted.

Kernel special forms (case, if, quote, raise, …) are suppressed as call refs — they are syntax, and on plug they were ~1,900 refs that could only ever resolve wrongly.

Validated on plug (S), phoenix (M) and firezone (L, 2,111 files): extraction PASS on all three, 137/144 route→action edges resolved at 100% precision on firezone, node/edge counts stable across re-index and incremental sync. Agent A/B (sonnet/high, 2 runs/arm) takes Read to ~0 and cuts tool calls 4-8x on every repo; wall-clock only improves on the large repo, which is recorded honestly in the coverage playbook.

Grammar is the tree-sitter-wasms tree-sitter-elixir build (ABI 14), health-checked — no vendored wasm needed.

Claude-Session: https://claude.ai/code/session_013Bsi9EH64kMisnik4E1gf7