Mesh/API parity for hybrid and layered retrieval

[marklubin]

Problem

Local Synix retrieval behavior is ahead of the current Mesh API path. Once the local runtime/tool API is stable, Mesh should match supported retrieval semantics so remote integrations do not drift from local behavior.

Scope

In scope:

• parity for supported keyword, semantic, hybrid, and layered retrieval modes
• parity between local runtime results and Mesh or HTTP results
• docs clarifying supported and unsupported parity cases

Out of scope:

• blocking the first local runtime milestone on Mesh support
• benchmark-specific study logic

Dependencies

• Depends on Python-local runtime/tool API for snapshot-scoped banks #82

Acceptance Criteria

• Supported retrieval modes behave equivalently across local runtime and Mesh
• Parity gaps are documented where exact equivalence is not possible

Required Automated E2E Test

Run the same retrieval cases through the local runtime and Mesh API, then compare returned refs and mode behavior for supported retrieval modes.

Docs Updates Required

• Mesh/runtime parity notes
• supported retrieval-mode matrix

Demo Or Template Follow-On

Record a follow-on extension to an existing mesh demo showing parity with the local runtime for hybrid and layered retrieval.