## What changed
### scripts/bb-mail-shim.mjs (new)
Translates bd mail delegate calls into bb agent coordination commands.
bd mail delegates by prepending the configured command to all args, so
this shim bridges the interface mismatch between bd mail (gt-mail style)
and bb agent (--agent/--from flags required).
Command mappings:
bd mail inbox [...] → bb agent inbox --agent $BB_AGENT [...]
bd mail send --to foo [...] → bb agent send --from $BB_AGENT --to foo [...]
bd mail read <msg-id> → bb agent read --agent $BB_AGENT --message <msg-id>
bd mail ack <msg-id> → bb agent ack --agent $BB_AGENT --message <msg-id>
bd mail <other> [...] → bb agent <other> [...] (passthrough)
Agent identity injected automatically from BB_AGENT env var (primary) or
BD_ACTOR env var (fallback). Caller can override --from by supplying it
explicitly in bd mail send args. Falls back with clear error messages if
bb is not in PATH or BB_AGENT/BD_ACTOR is unset.
### scripts/session-preflight.mjs (updated)
Added mail delegate auto-configuration step after successful bb resolution:
- Calls: bd config set mail.delegate "node <abs-path-to-bb-mail-shim.mjs>"
- Uses absolute path to shim resolved relative to session-preflight.mjs
- Reports mail.configured + mail.delegate + usage note in output JSON
- Graceful failure if shim missing, bd config set fails, or bb not found
- Added mail: null to all error branches for consistent output shape
## Verification
Tested end-to-end on this machine:
export BB_AGENT=silver-scribe
node session-preflight.mjs # → ok:true, mail.configured:true
bd mail send --to silver-scribe --bead beadboard-izs.5 \
--category INFO --subject "test" --body "pipeline verified"
bd mail inbox # → Inbox (1): [msg_...] INFO: test
All commands exit 0. Delegate persisted via bd config get mail.delegate.
## Bead: beadboard-izs.5 (closed)
## Also closed: beadboard-izs.2 — bb agent already in global CLI (feat(cli) commit)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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