Add release note for local split routing

docs/release-note-local-customization.md

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+# Release Note: Local Split-Routing Customization
+
+This note explains what the local customization changed, why it was needed, and why embeddings looked "broken first, then fixed later".
+
+## Summary
+
+The local customization solved a routing mismatch between:
+
+- the main OpenSpace LLM path
+- the skill-router embedding path
+- the Codex Desktop sidecar path
+
+The important result is:
+
+- OpenSpace main inference can continue using the local OpenAI-compatible gateway and `gpt-5.4`
+- skill-router embeddings no longer depend on that gateway exposing `/v1/embeddings`
+- Codex Desktop sidecar evolution stays isolated from the user's main Desktop session
+
+## What Was Wrong Before
+
+The main provider path was already usable for normal OpenSpace LLM calls:
+
+- `/v1/chat/completions`
+- `/v1/responses`-compatible workflows
+
+But the skill router has a separate semantic re-rank stage that tries to call:
+
+- `POST /v1/embeddings`
+
+The current local gateway worked for the main LLM path, but did not provide a working embeddings endpoint for this use case.
+
+So the real state before the fix was:
+
+- main OpenSpace task execution: usable
+- skill-router semantic embeddings: degraded or unavailable
+- Desktop sidecar: usable for LLM tasks, but still inherited the embedding weakness
+
+## Why It Looked Like "Embeddings Started Working"
+
+Embeddings did **not** start working on the same remote provider endpoint.
+
+What changed was the routing.
+
+Originally:
+
+- main LLM and skill embeddings were effectively expected to succeed through the same OpenAI-compatible path
+
+After the fix:
+
+- main LLM stayed on the provider path
+- skill embeddings were routed to a different backend
+
+For the current local setup, that different backend is:
+
+- `fastembed`
+- model: `BAAI/bge-small-en-v1.5`
+
+So the correct explanation is:
+
+- the remote embeddings path was not fixed
+- the system was changed so it no longer needed that remote embeddings path
+
+## What Was Implemented
+
+### 1. Split routing for skill embeddings
+
+Skill embedding generation now supports:
+
+- `OPENSPACE_SKILL_EMBEDDING_BACKEND=local`
+- `OPENSPACE_SKILL_EMBEDDING_BACKEND=remote`
+- `OPENSPACE_SKILL_EMBEDDING_BACKEND=auto`
+
+This was implemented in:
+
+- `openspace/cloud/embedding.py`
+- `openspace/skill_engine/skill_ranker.py`
+
+Effect:
+
+- the main LLM provider and the skill embedding backend are now decoupled
+
+### 2. Local embedding support
+
+Added `fastembed` as a project dependency and enabled local skill embeddings.
+
+Effect:
+
+- the skill router can still do semantic vector re-rank even when the LLM provider does not expose `/v1/embeddings`
+
+### 3. Launcher propagation
+
+Updated launchers so the new embedding settings are passed through consistently:
+
+- `scripts/openspace.sh`
+- `scripts/codex-openspace`
+- `scripts/codex-desktop-evolution`
+
+Effect:
+
+- CLI, isolated Codex profile, and Desktop sidecar all use the same split-routing model
+
+### 4. Sidecar isolation kept intact
+
+The Desktop sidecar still runs in an isolated overlay profile and does not overwrite the main Codex Desktop environment.
+
+Effect:
+
+- the user can keep their normal Desktop workflow
+- OpenSpace evolution still uses the provider-backed sidecar path
+- embedding config does not leak back into the main Desktop session
+
+## Current Effective Routing
+
+### Main LLM path
+
+- model: `gpt-5.4`
+- API base: `http://127.0.0.1:8080/v1`
+- source: `OPENSPACE_LLM_*`
+
+### Skill-router embedding path
+
+- backend: `local`
+- model: `BAAI/bge-small-en-v1.5`
+- source: `OPENSPACE_SKILL_EMBEDDING_*`
+
+### Desktop sidecar
+
+- still isolated through `scripts/codex-desktop-evolution`
+- uses the same split routing internally
+
+## Practical Result
+
+This local customization solved three concrete problems:
+
+1. OpenSpace no longer treats "main LLM works" and "embeddings work" as the same thing.
+2. Skill routing quality is preserved even when the LLM provider has no usable `/v1/embeddings`.
+3. Codex Desktop sidecar evolution keeps using provider tokens without polluting the main Desktop environment.
+
+## Short Version
+
+Before:
+
+- one path was effectively assumed to do both LLM and embeddings
+- the provider could handle the LLM part
+- the embedding part was weak or unavailable
+
+Now:
+
+- LLM still goes through the provider
+- embeddings go through local fastembed
+- sidecar remains isolated
+
+That is why it first looked broken and later looked fixed.
+
+It was not a provider repair.
+It was a routing repair.