feat: add built-in terminal and command execution infrastructure

Cargo.toml

@@ -1,5 +1,6 @@
 [workspace]
 members = [
+  "crates/chitin-builtin-shell",
   "crates/chitin-command",
   "crates/chitin-cli",
   "crates/chitin-bio",
@@ -8,6 +9,7 @@ members = [
   "crates/chitin-databases",
   "crates/chitin-desktop",
   "crates/chitin-molecule-renderer",
+  "crates/chitin-terminal",
   "crates/chitin-ui",
   "crates/chitin-wgpu",
   "crates/chitin-wasm",

assets/fonts/cascadia-mono/LICENSE

@@ -0,0 +1,94 @@
+Copyright (c) 2019 - Present, Microsoft Corporation,
+with Reserved Font Name Cascadia Code.
+
+This Font Software is licensed under the SIL Open Font License, Version 1.1.
+This license is copied below, and is also available with a FAQ at:
+http://scripts.sil.org/OFL
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded, 
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
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+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
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+in the appropriate machine-readable metadata fields within text or
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+3) No Modified Version of the Font Software may use the Reserved Font
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+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
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+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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+OTHER DEALINGS IN THE FONT SOFTWARE.

crates/chitin-builtin-shell/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "chitin-builtin-shell"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+
+[dependencies]
+chitin-command = { path = "../chitin-command" }
+chitin-databases = { path = "../chitin-databases" }
+chitin-terminal = { path = "../chitin-terminal" }
+clap = { version = "4.6", features = ["derive"] }
+thiserror = "2.0"
+
+[dev-dependencies]
+tokio = { version = "1.52", features = ["macros", "rt"] }
+
+[lints]
+workspace = true

crates/chitin-builtin-shell/src/event.rs

@@ -0,0 +1,59 @@
+//! Observable events emitted by a built-in shell session.
+
+use std::sync::Arc;
+
+use chitin_command::CommandExecutionEvent;
+
+use crate::{ShellCommandId, ShellExecutionRecord, ShellExecutionStatus};
+
+/// A state transition emitted by a built-in shell session.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum ShellEvent {
+  /// A parsed command was accepted as the active submission.
+  Submitted(ShellExecutionRecord),
+  /// A portable executor emitted progress, a message, or an artifact.
+  CommandExecution {
+    /// Shell-local identity of the active submission.
+    id: ShellCommandId,
+    /// Frontend-neutral event emitted by the command executor.
+    event: CommandExecutionEvent,
+  },
+  /// The active command entered a new shell lifecycle state.
+  StateChanged {
+    /// Shell-local identity of the affected submission.
+    id: ShellCommandId,
+    /// Current lifecycle state.
+    status: ShellExecutionStatus,
+  },
+}
+
+/// Cloneable callback receiving built-in shell events.
+#[derive(Clone)]
+pub struct ShellEventSink {
+  callback: Arc<dyn Fn(ShellEvent) + Send + Sync>,
+}
+
+impl ShellEventSink {
+  /// Creates a shell event sink from a thread-safe callback.
+  pub fn new(callback: impl Fn(ShellEvent) + Send + Sync + 'static) -> Self {
+    Self {
+      callback: Arc::new(callback),
+    }
+  }
+
+  /// Emits one event to the shell host.
+  pub fn emit(&self, event: ShellEvent) {
+    (self.callback)(event);
+  }
+
+  /// Creates a sink that deliberately discards every event.
+  pub fn silent() -> Self {
+    Self::new(|_| {})
+  }
+}
+
+impl Default for ShellEventSink {
+  fn default() -> Self {
+    Self::silent()
+  }
+}