This is a perfect balance of safety and minimalism. Defaulting to versioned
saves ensures you never lose a good state due to an accidental overwrite or a
bugged execution loop, while the environment overrides keep it lightweight for
constrained systems (like a browsers LocalStorage or a tiny LXC container).
Here is how we can implement this rolling backup strategy into the runtime
architecture.
Environment-Aware Versioning
We can inject a simple configuration object into the VM when it boots. The
deterministic runtime reads this config to decide how to handle the file
writes when the program yields.
 * MAX_BACKUPS > 0 (Rolling Window): Before saving the new state, the runtime
renames the current chrono_cell.md to chrono_cell.1.md. If chrono_cell.1.md
already exists, it gets pushed to .2.md, and so on, up to the limit. The
oldest version drops off.
 * MAX_BACKUPS = 0 (Strict Minimalist): The runtime performs a direct,
in-place overwrite of the fso-state block in the single file. No history is
kept.
 * MAX_BACKUPS = -1 (Full Audit Trail): Every save generates a new sequential
timestamped file.
Here is how that looks in the initialization:
/ Environment config passed in by the host (Node CLI, Browser, etc.)
const envConfig = {
    MAX_BACKUPS: process.env.FSO_MAX_BACKUPS || 3, // Keep last 3 states by
default
    WORKING_DIR: './deploy/sessions/'
};

const vm = new SemanticVM(envConfig);

/ The host environment's save handler
vm.onYield = (currentState, rawCode) => {
    const newFileContent = constructEnvelope(currentState, rawCode);
    
    if (envConfig.MAX_BACKUPS === 0) {
        fs.writeFileSync('program.md', newFileContent); // Direct overwrite
    } else {
        shiftRollingBackups('program.md', envConfig.MAX_BACKUPS);
        fs.writeFileSync('program.md', newFileContent);
    }
};

Execution I/O Strategy
Because this self-modifying file updates every time the program yields for
input (which happens constantly in a REPL or game loop), the file I/O needs to
be instantaneous.
It is crucial to keep this active execution directory strictly local. You
should avoid pointing the working directory to a folder monitored by live
background synchronization tools (like Google Drive desktop clients). The
rapid, sequential creation of state_1, state_2, and state_3 files can trigger
severe latency spikes, file locks, or race conditions from the sync client
trying to upload partial states.
Instead, letting the VM run locally and managing archival backups of the final
.md files via a manual script ensures the execution loop remains blistering
fast and entirely deterministic.
We now have the intent (Natural Language), the spec (Semantic Syntax), the
compiled artifact (FSO Envelope), and a highly portable, self-modifying
persistence model.
As a next step, would you like to map out the deterministic JavaScript lexer
that splits the fso blocks and parses the opcodes, or should we define a few
more of the core instruction commands (like mathematical operators) first?