feat(context): announce external context directories in the turn text

[luoxuanzao]

Summary

• External context directories were invisible to the agent: the CLI's own # Environment block is not part of Qoderian's system prompt, so the extra working directories never reached the model. The message you send right after adding or removing one now carries an <external_context> tag listing the current directories.
• The tag is appended to the user message (never the system prompt), so the prompt stays stable and the provider prefix cache is unaffected. It is sent once per change — additions, removals (rendered as (none)), and once after a session switch that never saw the current list. /compact keeps skipping context tags.
• The tag is registered with the existing XML context envelope (XML_CONTEXT_PATTERN, extractUserQuery), so message bubbles and history show the plain user text without it.

Verification

• npm run typecheck
• npm run lint
• npm run test — 165 suites / 3546 tests pass
• npm run build
• npm run release:check — Release 1.0.11 is ready
• npm run audit:prod — 0 vulnerabilities
• Real-app check in a live vault (two turns): the CLI session transcript records the <external_context> tag inside the user message and the model quotes the listed paths from it; the rendered user bubble contains no tag; a second message with an unchanged selection carries no tag

Safety

• No credentials, private vault content, internal URLs, or personal paths are included
• User-visible changes are documented in CHANGELOG.md

Co-authored-by: QoderAI (Qwen 3.8 Max) qoder_ai@qoder.com