fix(tools): stop telling the user USDC moved when it was account credits

[VickyXAI]

Follow-up to #162 (merged). Verified against main, not against the closed #156.

The problem

Six paid tool files have zero key-mode awareness and state the wrong payment instrument in 38 places.

file	sites	isKeyMode refs before
phone.ts	15	0
prediction.ts	9	0
videogen.ts	5	0
imagegen.ts	4	0
voice.ts	4	0
musicgen.ts	3	0
modal.ts, blockrun.ts	2	—

PredictionMarket  →  _$0.005 paid via x402._                  (signed nothing)
BuyPhoneNumber    →  ## Number provisioned ($5 USDC charged)  (wallet never moved)

The worst of the set are the approval prompts in ImageGen / VideoGen / phone. The human is asked to approve a spend in a currency the session does not use, and the model reads the same wrong sentence when it reasons about what it can still afford.

Before / after

[wallet mode]                                    [key mode]
## Number provisioned ($5.00 USDC charged)       ## Number provisioned (billed to account
                                                    credits — see Activity at user.blockrun.ai)
Buy a new US number for $5.00?                   Buy a new US number for $5.00?
  No USDC is spent if you cancel.                  No account credits are spent if you cancel.
_$0.0050 paid via x402._                         _Billed to account credits._

The split that matters

Runtime output (receipts, prompts, cancellations) calls the new src/payments/billing-copy.ts helpers, which read the mode at call time. invalidateKey() demotes a session mid-run after a 401 — a helper that captured the mode at import would keep claiming account credits while Franklin signed from the wallet again. There is a test for exactly that.

Static spec.description is built once at module load, before any mode is settled, and cannot re-render. Branching there would freeze whichever mode resolved first, so those strings are reworded to be true in both: Costs $0.001 per call, not Costs $0.001 USDC from the wallet. Likewise wallet-owned phone number → BlockRun-provisioned.

Key mode deliberately states no dollar amount on a receipt. The local figure is a catalog estimate; the account ledger is authoritative, so it points at Activity rather than inventing precision.

Verification

A regression fence scans every paid tool for an unconditional payment-rail string and names the offending file:line, so the next tool cannot reintroduce the class.

Mutation-tested — each fails a named test:

mutation	result
revert one phone.ts call site	fails the regression fence
make chargedNote ignore the mode	2 fail
memoise the mode at import	2 fail

730 local tests pass.

Credit

phone.ts had 5 of these fixed in #156 before it was closed as superseded; that approach is carried forward here and extended to the other six files.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Rm7cRGtC7wCofhYuHRo21h