Two new per-user preferences, `promptPrefix`/`promptSuffix`, hold free text
joined at the very start / end of the harness's assembled system prompt for
all agents (subagents included) — a per-deployment persona or behavioral rule
riding the harness's own prompt registry instead of session-log surgery:
- src/host/promptInjection.ts registers two global prompt sections through a
deferred `ctx.inject(['systemPrompt'], …)` (a composition without the
registry degrades to a no-op; the registration unwinds with this plugin's
fiber). Orders anchor on the harness's own section-order registry, so a
central renumbering keeps the prefix first and the suffix last. Text is
registered `interpolate: false`, so `{{...}}` in user text stays literal.
- The section text providers read the volatile config references the loader
rewrites in place on preference edits, so an edit applies from the next
turn without remounting the entry; new sessions carry the text from their
first turn through the harness's own system-prompt projection.
- The settings card grows two free-text rows (local draft, committed on blur
and on unmount; a host push never clobbers in-progress typing), zh/en
strings, and the served-value sanitize/degrade path for the string fields.
Verified against a running harness: the committed text persists in the
profile layer, and a new session's system prompt starts with the prefix and
ends with the suffix. docs/compatibility.md documents the seams, and the
compat matrix probes them on both supported lines.
bowenliang123
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