[plan] Document Copilot CLI 1.0.19 BYOK and new flags in engines.md

[github-actions]

Objective

Update docs/src/content/docs/reference/engines.md (and related reference pages) to document the significant new features introduced in Copilot CLI 1.0.19, with a focus on agentic workflow use cases.

Context

Issue #25014 tracks the 1.0.18 → 1.0.19 update. There is currently zero documentation coverage for BYOK, new CLI flags, and new environment variables relevant to gh-aw workflows.

Files to Modify

• docs/src/content/docs/reference/engines.md — primary target, add new flags and BYOK section
• docs/src/content/docs/reference/environment-variables.md — add new env vars
• Optionally create docs/src/content/docs/reference/byok.md if BYOK content warrants its own page

Approach

1. BYOK section in engines.md (or new byok.md): document COPILOT_PROVIDER_BASE_URL, COPILOT_PROVIDER_TYPE (openai / azure / anthropic), COPILOT_PROVIDER_API_KEY, COPILOT_PROVIDER_BEARER_TOKEN, COPILOT_PROVIDER_WIRE_API, and related token limit overrides. Include a usage example for Ollama/vLLM local testing.
2. Agentic flags section: document flags directly relevant to gh-aw workflows:
   • --no-ask-user — fully autonomous runs
   • --secret-env-vars[=vars...] — strip secrets from MCP server environments (security recommendation)
   • --output-format json — JSON/JSONL output for scripting
   • -s, --silent — minimal output for scripting with -p
   • --no-custom-instructions — disable AGENTS.md loading
   • --yolo — alias for --allow-all
   • --max-autopilot-continues <n> — cap continuation messages
3. Environment variables in environment-variables.md: add all new 1.0.19 env vars (see issue [ca] Update Copilot CLI: 1.0.18 → 1.0.19 (major new features) #25014 for the full list: COPILOT_AUTO_UPDATE, COPILOT_CUSTOM_INSTRUCTIONS_DIRS, COPILOT_OFFLINE, PLAIN_DIFF, USE_BUILTIN_RIPGREP, and the BYOK provider vars).
4. Models list: update the available models list (Claude and GPT models from 1.0.19).
5. Offline mode: document COPILOT_OFFLINE=true for air-gapped/local testing scenarios.

Acceptance Criteria

• BYOK configuration is documented with at least one complete example (e.g., using Ollama)
• All new flags relevant to agentic workflows are documented in engines.md
• All 14+ new environment variables are present in environment-variables.md
• Available models list is up to date
• --secret-env-vars usage is highlighted as a security recommendation for gh-aw workflows
• No broken links or references to 1.0.18-specific behaviour
  Related to [Daily Report] Documentation Quality Report — April 7, 2026 #25041

Generated by Plan Command for issue #25041 · ● 360.6K · ◷

• expires on Apr 9, 2026, 10:34 AM UTC

[github-actions]

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