Apis

        .checked_sub(fee)        .ok_or(ApisError::ArithmeticOverflow)?;     // Pre-CPI invariant — vault must hold exactly the locked price.    require!(        ctx.accounts.escrow_vault.amount == price,        ApisError::VaultAmountMismatch    );     // Build PDA signer seeds for the vault transfers + close.    let buyer_key = ctx.accounts.job.buyer;    let id_le = ctx.accounts.job.id.to_le_bytes();    let job_bump = ctx.accounts.job.bump;    let job_seeds: &[&[u8]] = &[b"job", buyer_key.as_ref(), &id_le, &[job_bump]];    let signer_seeds = &[job_seeds];     let token_program = ctx.accounts.token_program.key();    let mint_decimals = ctx.accounts.usdc_mint.decimals;     // Payout to provider (omit if 0 — happens only at fee_bps == 10_000).    if payout > 0 {        let cpi_accounts = TransferChecked {            from: ctx.accounts.escrow_vault.to_account_info(),            mint: ctx.accounts.usdc_mint.to_account_info(),

1. Line 145 .checked_sub(fee): Uses checked arithmetic so overflow fails instead of wrapping.
2. Line 149 require!(: An explicit validation that aborts the instruction with an error.
3. Line 157 let job_bump = ctx.accounts.job.bump;: Uses the bump seed, the extra byte that pushes the derived address off the ed25519 curve.
4. Line 159 let signer_seeds = &[job_seeds];: Declares the PDA seeds. Anchor re-derives the address and rejects the account if it doesn't match.
5. Line 166 let cpi_accounts = TransferChecked {: A checked token transfer, which also verifies the mint and decimals.

        to: ctx.accounts.escrow_vault.to_account_info(),        authority: ctx.accounts.buyer.to_account_info(),    };    let cpi_ctx = CpiContext::new(ctx.accounts.token_program.key(), cpi_accounts);    transfer_checked(cpi_ctx, price_lamports_usdc, ctx.accounts.usdc_mint.decimals)?;     // Re-read the vault after the CPI; assert the exact amount we asked    // to transfer landed (catches partial-fill edge cases under    // Token-2022 transfer hooks, etc.).    ctx.accounts.escrow_vault.reload()?;    require!(        ctx.accounts.escrow_vault.amount == price_lamports_usdc,        ApisError::VaultAmountMismatch    );     let now = Clock::get()?.unix_timestamp;    let deadline = now        .checked_add(deadline_offset_secs)        .ok_or(ApisError::InvalidDeadline)?;     let job = &mut ctx.accounts.job;    job.set_inner(Job {        id,        buyer: ctx.accounts.buyer.key(),

1. Line 112 let cpi_ctx = CpiContext::new(ctx.accounts.token_program.key(), cpi_accounts);: Makes a cross-program invocation into another program.
2. Line 113 transfer_checked(cpi_ctx, price_lamports_usdc, ctx.accounts.usdc_mint.decimals)?;: A checked token transfer, which also verifies the mint and decimals.
3. Line 119 require!(: An explicit validation that aborts the instruction with an error.
4. Line 124 let now = Clock::get()?.unix_timestamp;: Reads on-chain time from the Clock sysvar.
5. Line 126 .checked_add(deadline_offset_secs): Uses checked arithmetic so overflow fails instead of wrapping.

    /// Buyer cancelling. Receives the USDC refund + vault/Job rent.    #[account(mut)]    pub buyer: Signer<'info>,     /// Singleton config — only consulted for `usdc_mint`.    #[account(seeds = [b"config"], bump = config.bump)]    pub config: Account<'info, GlobalConfig>,     /// Job to cancel. Must be the buyer's, Funded, and gets closed    /// (rent → buyer) via Anchor's `close = buyer`.    #[account(        mut,        close = buyer,        seeds = [b"job", buyer.key().as_ref(), job.id.to_le_bytes().as_ref()],        bump = job.bump,        has_one = buyer @ ApisError::WrongBuyer,        constraint = job.status == JobStatus::Funded @ ApisError::JobNotFunded,    )]    pub job: Account<'info, Job>,     /// USDC mint — matches config.usdc_mint.    #[account(address = config.usdc_mint @ ApisError::WrongMint)]    pub usdc_mint: Account<'info, Mint>,

1. Line 27 pub buyer: Signer<'info>,: Requires this account to have signed the transaction.
2. Line 30 #[account(seeds = [b"config"], bump = config.bump)]: Declares the PDA seeds. Anchor re-derives the address and rejects the account if it doesn't match.
3. Line 30 #[account(seeds = [b"config"], bump = config.bump)]: Uses the bump seed, the extra byte that pushes the derived address off the ed25519 curve.
4. Line 34 /// (rent → buyer) via Anchor's `close = buyer`.: Closes the account at the end of the instruction and refunds its lamports.
5. Line 40 has_one = buyer @ ApisError::WrongBuyer,: Checks that a stored pubkey field matches the passed account.

/// - `job.provider == provider.key()` (the job was targeted to this///   provider, not someone else)/// - `job.status == Funded` (no double-accept; no jumping a non-funded///   job)#[derive(Accounts)]pub struct AcceptJob<'info> {    /// Provider's authority — must match `provider.authority`.    pub authority: Signer<'info>,     /// Provider PDA the signer owns.    #[account(        seeds = [b"provider", authority.key().as_ref()],        bump = provider.bump,        has_one = authority @ ApisError::WrongProviderAuthority,        constraint = provider.status == ProviderStatus::Active            @ ApisError::ProviderNotActive,    )]    pub provider: Account<'info, Provider>,     /// Job to accept. Must target this provider and be in `Funded`    /// status. We rederive the PDA from `job.buyer` / `job.id` to make    /// sure the caller hasn't substituted a fake account at the same    /// type — Anchor will deserialise + then verify seeds match.    #[account(

1. Line 20 pub authority: Signer<'info>,: Requires this account to have signed the transaction.
2. Line 24 seeds = [b"provider", authority.key().as_ref()],: Declares the PDA seeds. Anchor re-derives the address and rejects the account if it doesn't match.
3. Line 25 bump = provider.bump,: Uses the bump seed, the extra byte that pushes the derived address off the ed25519 curve.
4. Line 26 has_one = authority @ ApisError::WrongProviderAuthority,: Checks that a stored pubkey field matches the passed account.