* fix(security): keep channel-metadata and install-policy truncation surrogate-safe
channel-metadata.ts and install-policy.ts both had private truncateText
functions using String.prototype.slice(0, N) on user-visible text.
channel-metadata is explicitly user-controlled untrusted content that gets
injected into LLM prompt context -- a dangling surrogate from unsafe
truncation would corrupt the prompt with invalid Unicode, affecting token
counting and potentially LLM response quality.
Replace .slice(0, ...) with truncateUtf16Safe(...) in both files so the
truncation point always falls on a complete code-point boundary.
Add test coverage for buildUntrustedChannelMetadata with emoji at both
the entry-level (400-char) and outer (800-char) truncation boundaries.
* test(security): prove UTF-16 truncation boundaries
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Co-authored-by: Peter Steinberger <steipete@gmail.com>
zw-xysk
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