Faber hands policy: haiku delegation for context-heavy mechanical work

[yihanzhu]

Context

Faber's frontier session re-processes its whole context every turn, so bulky reads (CI logs, PR diffs, review threads) inlined into the manager session get re-billed for the rest of the session. Approved design: a "hands" tier (FABRICA_HANDS_MODEL, haiku) acts as a context firewall. Depends on the config/models.conf foundation issue.

Spec

• manager/CLAUDE.md + templates/faber-command.md: add a delegation policy —
  • Delegate to a FABRICA_HANDS_MODEL subagent: context-heavy reads and multi-step polling (watch CI to completion and summarize failures, fetch+summarize PR diffs, collect review threads, bulk gh queries).
  • Keep inline: single quick writes (posting one comment, one label operation, one merge click) — the content is Faber's reasoning anyway and a subagent spin-up costs more than the call.
  • Hands agents must return key raw lines plus a short summary, never conclusions alone, so Faber's decisions rest on evidence.
• Rule of thumb to include: delegate when (tokens the action would add to Faber's context) x (expected remaining turns) exceeds the cost of a hands spawn.

Sync note

Prompt-only change — takes effect ONLY after re-running scripts/install.sh. Call this out in the PR description.