feat: USDC quote-mint support for the launch path (create_v2 + buy_v2)

[HankWyatt]

Summary

Adds USDC (non-native quote-mint) support to the launch path — createV2Instruction, a new buyV2 builder, and createV2AndBuyInstructions — mirroring the official @pump-fun/pump-sdk API shape. Motivated by pump.fun enabling USDC as a quote mint (2026-05-21) via the V2 instructions. The SDK already had read/display USDC support (channel-bot); this adds the minting / buying side.

Fully additive & backward-compatible: every new param defaults to wrapped SOL, so existing SOL callers are byte-identical — the entire existing test suite passes unchanged.

What's included

• quoteMint? / quoteTokenProgram? (default wSOL / SPL Token) on createV2Instruction, buyInstructions, getBuyInstructionRaw, and createV2AndBuyInstructions (plus an explicit quoteAmount cap). For a non-native quote, createV2Instruction appends the 3 quote remaining accounts and the buy path routes to buy_v2.
• New buyV2 builder (the 27-account V2 buy).
• buy_v2 added to the bundled IDL (src/idl/pump.json + pump.ts) — it was missing.
• New src/quoteMints.ts — USDC_MINT, QUOTE_MINTS, isNativeQuote.
• BUYBACK_FEE_RECIPIENTS / pickBuybackFeeRecipient — a clarity alias over the existing breaking-recipient set (verified identical to the 8 official buyback recipients).
• OnlinePumpSdk wrappers forward the quote params.
• buyInstructions (USDC) prepends the user's base + quote ATA creates (the program does not init the user's ATAs).
• 21 new offline unit tests (fixture-based, no RPC — per CONTRIBUTING): SOL byte-identity, the 3 create_v2 remaining accounts, the full 27-account buy_v2 layout, buy routing, ATA creation, the quoteAmount cap, and the tx-size/ALT constraint.
• scripts/devnet-usdc-smoke.ts — a devnet/simulate verification harness.

Notes: the base mint stays Token-2022; the quote side uses the legacy SPL Token program (even for USDC). bondingCurve.ts is unchanged — the math is quote-agnostic.

Verified on devnet

• create_v2 (USDC-paired) broadcast succeeded: tx → coin mint HADmcDGudvWyCTSBe5KKiw3KcMz7xuJnhePmh7CxdB5G.
• buy_v2 (USDC) simulated against the live program: all 27 accounts accepted, the program init_if_needed-created the program-side quote ATAs, ran fee computation, and failed only at the quote TransferChecked with insufficient-funds (the test wallet held 0 quote token) — i.e. the account layout is correct.

Address Lookup Table note

A USDC createV2AndBuyInstructions transaction (~1361 bytes / 32 accounts) exceeds the 1232-byte single-transaction limit and must be sent as a v0 transaction with an Address Lookup Table (with one, it compiles to ~605 bytes; the smoke script demonstrates this). The SOL path fits without one. The builders return instructions; ALT assembly is left to the sender, matching the existing pattern.

Tests

npm test → 12 suites / 295 tests pass (21 new USDC tests; the existing suite is unchanged).