docs: sync dewey DEWEY_SYNTHESIS_ENDPOINT documentation

[jflowers]

What Changed

Dewey now has a dedicated DEWEY_SYNTHESIS_ENDPOINT environment variable for configuring the synthesis (LLM generation) provider endpoint independently from the embedding endpoint.

Previously, the synthesis endpoint incorrectly reused DEWEY_EMBEDDING_ENDPOINT. This was a bug tracked in unbound-force/dewey#71.

New env var

• DEWEY_SYNTHESIS_ENDPOINT: Overrides the synthesis provider endpoint. Fallback chain: DEWEY_SYNTHESIS_ENDPOINT → OLLAMA_HOST → http://localhost:11434.

Precedence asymmetry

Unlike embedding (where DEWEY_EMBEDDING_ENDPOINT env var overrides config.yaml), the synthesis path gives config.yaml highest precedence. Env vars are consulted only when config.yaml does not specify a synthesis section.

Affected Pages

• Provider configuration documentation (endpoint resolution chains)
• Environment variable reference tables
• Any pages documenting DEWEY_EMBEDDING_ENDPOINT that mention synthesis behavior

What Needs Updating

• Add DEWEY_SYNTHESIS_ENDPOINT to env var reference tables
• Document the synthesis endpoint resolution chain
• Note the precedence asymmetry between embedding and synthesis paths
• Remove any references to DEWEY_EMBEDDING_ENDPOINT controlling synthesis behavior

[jflowers]

Triage: VALID — Unanimous (5/5)

Category: docs | Objectivity: OBJECTIVE | Split: Not needed

All five Divisor agents confirm this is a legitimate documentation sync request for the DEWEY_SYNTHESIS_ENDPOINT env var, filed as task 3.2 of the synthesis-endpoint-env OpenSpec change. All four technical claims verified against source code (llm/config.go):

1. ✅ New DEWEY_SYNTHESIS_ENDPOINT env var exists (llm/config.go:21)
2. ✅ Precedence chain: config.yaml > DEWEY_SYNTHESIS_ENDPOINT > OLLAMA_HOST > default
3. ✅ Asymmetry with embedding resolution documented in AGENTS.md
4. ✅ Auto-scheme-prepend in normalizeSynthesisEndpoint()

Scope: content/docs/dewey/configuration/ (env vars reference + provider config guide)

Notes from panel:

• Adversary: Docs should note that DEWEY_SYNTHESIS_ENDPOINT routes synthesis traffic to arbitrary hosts — users should understand the data-flow implication
• Testing: 10+ test cases in llm/provider_test.go back every documented behavior
• Guard: No intent drift — issue faithfully reflects implementation

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Divisor Review Panel

Agent	Verdict	Category	Objectivity
Adversary	VALID	docs	OBJECTIVE
Architect	VALID	docs	OBJECTIVE
Guard	VALID	docs	OBJECTIVE
SRE	VALID	docs	OBJECTIVE
Testing	VALID	docs	OBJECTIVE