Zero-fee routing test set (`fee_bps = 0`, recipient set)

[nanaf6203-bit]

Problem Statement
The fee logic was reviewed for the fee_bps > 0 cases. The
fee_bps = 0 case (no fee) but fee_recipient is still set — does the
contract skip the fee transfer cleanly? The path is short, partly
covered.

Why it matters
A bug here means users are tipped 100% with fee logic still touching
storage. Risk of confused book-keeping.

Acceptance Criteria

• Tests for: zero fee no recipient, zero fee with recipient, zero
  fee recipient changed mid-session.
• No fee_recipient panic for these.

Files/Modules Likely Affected

• src/test.rs

Difficulty Easy. Estimated Effort XS.

Labels
area:testing, area:fee, priority:medium,
good-first-issue

---

F. Testing — Coverage / Property

---

Imported from docs/open-issues-draft.md as draft issue #33 (commit 7becd4b). Original draft-order cross-references in this body have been remapped to current GitHub issue numbers at import time.

[GBOYEE]

Hi team — I'd like to take this on as part of the GrantFox campaign. I'll add the tests and open a PR shortly.