SeaShell is built to run more than one coding session at the same time without the sessions overwriting each other's work or state. Each session runs as its own runtime instance keyed to the directory it works in, and any state that sessions share is protected by locks so two sessions can never half-write the same record. That means you can keep several agents or terminals going at once, including across different git worktrees of the same repository, and each one stays consistent. SeaShell runs as a single self-contained binary.
The problem with concurrent AI sessions
Many terminal agents assume one active session per project. Open a second session and they can contend for the same files and state, so one session's action overwrites another's. SeaShell is designed for concurrency from the start.
When two sessions share a single project directory, an action in one, such as writing history, saving config, or removing a working copy, can silently overwrite or invalidate what the other is doing. The failure shows up as lost edits, corrupted session state, or a crash. SeaShell treats concurrent sessions as the normal case rather than an edge case, so parallel work is safe by construction.
Per-directory runtime isolation
SeaShell keys each live session to the working directory it operates in and gives that directory its own runtime instance. Multiple instances coexist in one process, each with its own language servers, snapshots, and permission boundary.
Because each directory, including each git worktree checkout, gets its own isolated instance, two sessions running in different places do not share the live runtime state that would otherwise collide. Concurrent loads of the same instance are deduplicated rather than raced, so starting several sessions at once is deterministic instead of a scramble.
Locking that prevents state bleed
For the durable state that sessions genuinely share, SeaShell serializes access with locks. In-process reentrant read and write locks guard each storage record, and a cross-process file lock coordinates work across separate SeaShell processes.
The cross-process lock is a careful directory-based lock with heartbeats, stale-owner recovery, and process metadata, used for config writes, plugin installs, and other shared operations. The combination means concurrent sessions in different worktrees still write into shared repo state safely: the locks make that contention correct rather than destructive. Each instance also keeps its own permission boundary, so isolation holds for what an agent is allowed to do, not just for the files it writes.
Frequently asked questions
- Can I run multiple SeaShell sessions at the same time?
- Yes. SeaShell is built for concurrency: it runs multiple sessions in one process, each isolated by working directory, and guards shared state with locks.
- Will one session overwrite another session's work?
- No. Each session runs as its own per-directory instance, and shared writes are serialized by in-process and cross-process locks, so sessions do not clobber each other.
- Does this work across git worktrees of the same repo?
- Yes. Sessions in different worktrees get separate runtime instances, and any state they share in the repo is lock-protected, so concurrent worktree sessions stay consistent.
- Is the concurrency safe on Windows?
- Yes. SeaShell runs natively on Windows, and its locking and per-directory isolation apply the same way as on macOS and Linux.
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