Solana Bootcamp Arc 11: How Cross-Program Invocations Enable Composable Programs

Arc 11 of the Solana developer bootcamp covered Days 71–77 of Epoch 3, focusing on Cross-Program Invocations (CPIs), which allow one Solana program to call another within the same transaction. CPIs are central to Solana's composability, as programs like the System Program and Token-2022 each own and enforce rules over specific operations, requiring other programs to invoke them rather than replicate their logic. The arc began with a simple SOL transfer exercise where an Anchor program delegated the actual transfer to the System Program instead of modifying balances directly. A key security principle explored was that CPIs cannot escalate account privileges — writable access and signer authority must already exist in the original transaction. Later sessions extended the model to token minting, introducing Program Derived Addresses as a source of signing authority for inner calls.