fix: mail send prefix mismatch — generate database-prefixed IDs

[DreadPirateRobertz]

Summary

• gt mail send was broken — all sends failed with "prefix mismatch: database uses 'hq-' but ID 'msg-...' doesn't match"
• Root cause: GenerateID() always produced msg-* IDs but HQ database requires hq- prefix
• Added GeneratePrefixedID() that reads the database prefix from metadata.json
• Fixed both sendToSingle() in mail router and the handoff direct-create path

Test plan

• Built and installed locally
• gt mail send overseer/ -s "Test" -m "Test" succeeds (was failing before)
• Messages appear in inbox with correct hq-wisp-* IDs
• Run go test ./internal/mail/...
• Run go test ./internal/beads/...

🤖 Generated with Claude Code

[codecov-commenter]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
7426	2	7424	34

View the top 2 failed test(s) by shortest run time

::TestMain

Stack Traces | 0s run time

FAIL	github..../gastown/internal/convoy [build failed]

::TestMain

Stack Traces | 0s run time

FAIL	github..../gastown/internal/daemon [build failed]

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[DreadPirateRobertz]

Reviewed — clean, well-scoped fix.

Root cause correctly identified: GenerateID() produces msg-* IDs but HQ database enforces hq-* prefix validation. GeneratePrefixedID(prefix, isWisp) properly generates database-compatible IDs.

Code looks correct:

• sendToSingle() condition msg.ID == "" || strings.HasPrefix(msg.ID, "msg-") correctly overwrites pre-existing invalid msg-* IDs
• Both sendToSingle and sendHandoffMail paths are fixed
• ConfigPrefixFromDir with "hq" fallback is safe for HQ-only mail routing

Minor nit (non-blocking): readBeadsPrefix in router.go is a one-liner wrapper around beads.ConfigPrefixFromDir — could call it directly. Not worth blocking.

LGTM.

[DreadPirateRobertz]

Code Review: PR #2211 — Mail Send Prefix Mismatch Fix

Reviewed by: zhora (crew)

RECOMMEND CLOSE. This bug was already fixed on main (commit 0b091f2) via a cleaner approach: removing explicit --id from bd create entirely. This PR would reintroduce --id and conflict with the merged fix. PR is in CONFLICTING state confirming this.

[DreadPirateRobertz]

Closing — the prefix mismatch issue has been resolved differently on main. The mail router now lets bd auto-generate IDs with the correct prefix instead of passing explicit --id flags. The GenerateID() function is only used for in-memory tracking, not persisted to beads.