docs(adapters): fix user-doc inaccuracies (closes spec PR #148 audit)

[mmercuri]

Summary

Fixes three pre-existing inaccuracies in the user-facing adapter docs that
spec PR #148 (docs/adapters/embedding.md, docs/adapters/benchmark_import.md)
surfaced. PR #148 added new spec docs and called out the inaccuracies in
those new specs but did NOT modify the inaccurate user docs. This PR
closes that loop.

Base note: This PR is based on feat/instrument-frameworks-agents
(PR #97) because the user docs being fixed (docs/adapters/frameworks-embedding.md
and docs/adapters/frameworks-benchmark_import.md) only exist on that
branch — they are not yet in main. Targeting that branch keeps this
PR's diff clean (a single commit, two file changes).

Inaccuracies fixed

1. docs/adapters/frameworks-embedding.md — wrong event name

Was: "emit embedding.create and vector_store.query events"
Now: "emit embedding.create and retrieval.query events"

Source emits the literal string "retrieval.query":

• src/layerlens/instrument/adapters/frameworks/embedding/vector_store_adapter.py:167 (Pinecone wrapper)
• src/layerlens/instrument/adapters/frameworks/embedding/vector_store_adapter.py:199 (Weaviate wrapper)
• src/layerlens/instrument/adapters/frameworks/embedding/vector_store_adapter.py:233 (Chroma wrapper)

Updated 2 occurrences (intro + Events-emitted table). Added a taxonomy
note clarifying that vector-store retrieval is normalized to
retrieval.query regardless of backend, with cross-reference to the
canonical spec at docs/adapters/embedding.md.

2. docs/adapters/frameworks-benchmark_import.md — non-existent heuristic

Was: "When no mapping is provided, the adapter applies a small set of
automatic heuristics (case-insensitive name match against the canonical
fields)."
Now: Explicit-mapping-only behavior, with v1.8 roadmap reference.

Source short-circuits when no mapping is provided:

# src/layerlens/instrument/adapters/frameworks/benchmark_import/adapter.py:423-434
@staticmethod
def _apply_schema_mapping(
    record: dict[str, Any],
    mapping: dict[str, str] | None,
) -> dict[str, Any]:
    """Apply field name mapping to a record."""
    if not mapping:
        return record
    ...

There is no case-insensitive matching, no fuzzy aliasing — pass-through
only. v1.8 roadmap reference is consistent with spec PR #148 §7
("v1.8 — Schema-heuristic detection").

3. docs/adapters/frameworks-benchmark_import.md — implies BaseAdapter inheritance

Was: Title "Benchmark import framework adapter"; body grouped it with
"the other framework adapters", implying the runtime-instrumentation
contract (BaseAdapter lifecycle, capabilities, sinks).
Now: Title "Benchmark import (data importer)"; new architectural note
explicitly calls out the bare-class shape.

Source declares no superclass:

# src/layerlens/instrument/adapters/frameworks/benchmark_import/adapter.py:70
class BenchmarkImportAdapter:
    """
    Imports external benchmark datasets into Stratix evaluation spaces.
    ...

This matches the architectural carve-out in spec PR #148 §1 (the adapter
is a one-shot ETL pipeline, not a runtime instrumentation adapter — no
connect() / disconnect() lifecycle, no AdapterCapability enum, no
sinks, no telemetry events).

Out of scope (not changed)

The persistence section in frameworks-benchmark_import.md describes a
save_benchmark(metadata, records) store API, but the source actually
uses insert_row(table, row) (adapter.py:441-444). This is an
additional inaccuracy not in the original audit and was not requested
in the task scope. Recommend filing a follow-up issue.

Test plan

• Verified each source line cited above by reading the actual file
  content on the feat/instrument-frameworks-agents branch.
• Verified no remaining vector_store.query references in
  docs/, samples/, src/, or tests/ after the edit
  (grep -rn 'vector_store\.query' returns 0 matches).
• Cross-checked against PR docs(adapters): embedding + benchmark_import specs #148 spec framing for §1 (architectural
  note), §3.3 (event payload schema reference), and §7 (v1.8
  roadmap).
• Markdownlint not run (not installed in worktree); visually
  reviewed both files for broken markdown.

References

• Spec PR docs(adapters): embedding + benchmark_import specs #148 (docs/adapter-specs-embedding-benchmark-import branch)
• Source: src/layerlens/instrument/adapters/frameworks/embedding/vector_store_adapter.py
• Source: src/layerlens/instrument/adapters/frameworks/benchmark_import/adapter.py

[mmercuri]

Adding follow-up commit for the 4th inaccuracy (Persistence section save_benchmark vs insert_row) that agent a56bee25024184e15 surfaced during the original fix. Now consolidated in this PR per reviewer ergonomics.