ADR 0006: document txHash retention on delete

[heyitsStylez]

Parent

#68

What to build

Write docs/adr/0006-txhash-retention-on-delete.md documenting the invariant that deleteTrade must never remove a deleted trade's txHash from hw_synced_v1.

Cover:

• The invariant: txHash stays in the synced set after a trade is deleted
• The reason: the synced set is the sole guard against chain sync re-importing a trade the user intentionally removed
• The edge case: if ALL chain-imported trades are deleted, the boot migration clears the synced set and re-import will occur on next boot — this is a known, accepted limitation
• No code changes — documentation only

Acceptance criteria

• docs/adr/0006-txhash-retention-on-delete.md exists and follows the ADR format used by 0003–0005
• ADR states the invariant clearly: deleting a trade must not remove its txHash from hw_synced_v1
• ADR explains the reason: preventing chain sync re-import of intentionally deleted trades
• ADR acknowledges the boot-migration edge case (all chain trades deleted → synced set cleared → full re-import)
• No source files modified

Blocked by

None — can start immediately