//! Builder types, the [`Builder`] trait, and the parallel execution model.
//!
//! Each `[[builders]]` entry in `abbaye.toml` deserialises into a
//! [`BuilderEntry`] and is run as an independent Tokio task.  This module
//! owns the [`AnyBuilder`] enum (the TOML type-tag dispatch), the
//! [`LogEvent`] channel used for progress-bar updates, and the [`Builder`]
//! trait that every concrete builder must implement.
//!
//! ---
//!
//! # Parallel Builder Execution
//!
//! This section explains how Abbaye runs the `[[builders]]` entries defined in
//! `abbaye.toml` in parallel, how inter-builder dependencies are enforced, and
//! how the progress UI is kept in sync with the running tasks.
//!
//! ## Overview
//!
//! Every `[[builders]]` entry is executed as an independent Tokio async task.
//! Tasks are launched at the same time (via a shared `JoinSet`) and may
//! therefore run fully concurrently.  When a builder declares `depends_on`,
//! its task simply waits — without blocking any thread — until all named
//! prerequisites have completed successfully before invoking the underlying
//! build logic.
//!
//! ## Configuration Model
//!
//! ### `BuilderEntry`
//!
//! Each `[[builders]]` table in the TOML file deserialises into a
//! [`BuilderEntry`]:
//!
//! | Field        | Type              | Purpose                                                           |
//! |--------------|-------------------|-------------------------------------------------------------------|
//! | `builder`    | [`AnyBuilder`]    | Type-tagged union holding the builder's own config (flattened).   |
//! | `id`         | `Option<String>`  | Stable name that other builders can reference in `depends_on`.    |
//! | `depends_on` | `Vec<String>`     | IDs of builders that must succeed before this one starts.         |
//!
//! Example:
//!
//! ```toml
//! [[builders]]
//! type    = "cargo"
//! id      = "compile"
//!
//! [[builders]]
//! type       = "script"
//! script     = ["strip target/release/mybin"]
//! outputs    = ["target/release/mybin"]
//! depends_on = ["compile"]          # waits for the cargo builder above
//! ```
//!
//! ### `AnyBuilder` variants
//!
//! | TOML `type`  | Rust variant  | What it does                                              |
//! |--------------|---------------|-----------------------------------------------------------|
//! | `archive`    | `Archive`     | Creates a `.tar.gz` of the source tree.                   |
//! | `cargo`      | `Cargo`       | `cargo build --release`, optionally for multiple targets. |
//! | `cargo_doc`  | `CargoDoc`    | `cargo doc`.                                              |
//! | `markdown`   | `Markdown`    | Renders a directory of `.md` files to HTML.               |
//! | `script`     | `Script`      | Runs an arbitrary sequence of `sh -c` commands.           |
//!
//! ## Orchestration in `build_site` (`src/site.rs`)
//!
//! The entire builder pipeline lives inside `build_site`, in three phases.
//!
//! ### Phase 1 — Validation
//!
//! Before any task is spawned, two checks are performed:
//!
//! 1. **Reference check** — every string in `depends_on` must match an `id`
//!    of some other builder in the same config.  Unknown IDs are reported as a
//!    hard error immediately.
//!
//! 2. **Cycle detection** — a depth-first search visits the dependency graph
//!    and returns an error if a cycle is found.
//!
//! The DFS tracks three states per node: `0 = unvisited`, `1 = in the current
//! stack`, `2 = fully processed`.  Encountering a node in state `1` means
//! there is a back-edge, i.e. a cycle.
//!
//! ### Phase 2 — Completion channels
//!
//! For each builder that carries an `id`, a `tokio::sync::watch` channel is
//! created:
//!
//! ```text
//! watch::channel(None::<bool>)
//!          ↑
//!          └─ initial value: None  (pending)
//! ```
//!
//! The channel is later sent `Some(true)` (success) or `Some(false)`
//! (failure).  Dependents hold a cloned `Receiver` and call
//! `wait_for(|v| v.is_some())`, which suspends the task cooperatively until
//! the value changes.
//!
//! If a dependency's `watch::Sender` is dropped without ever sending a value
//! (e.g. the task panicked), `wait_for` returns an `Err`, which is treated as
//! a failure and the dependent is skipped.
//!
//! ### Phase 3 — Task spawning and collection
//!
//! All tasks are submitted to a single `tokio::task::JoinSet`.  Every task
//! follows the same lifecycle:
//!
//! - **Spawned** → waits for all declared dependencies.
//! - **Running** → all deps succeeded; the builder executes.
//! - **Skipped** → a dependency failed; returns `Ok(vec![])` and signals
//!   `Some(false)` so its own dependents also skip.
//! - **Done / Failed** → signals `Some(true)` or `Some(false)`.
//!
//! After all tasks finish, collected [`ArtifactPath`]s are classified:
//!
//! - **File** artifacts → `dist/` (distribution binaries, archives, etc.).
//! - **Directory** artifacts → `docs/` (rustdoc output, rendered Markdown, …).
//!
//! If any builder returned an error, the first error is propagated to the
//! caller after all spinners have settled, so the full UI is always rendered
//! to completion.
//!
//! ## Progress UI
//!
//! The UI is built with the `indicatif` crate.  Each builder task owns:
//!
//! - A **parent spinner** inserted *above* a shared summary bar.
//! - An **mpsc log channel** ([`LogSender`]) over which the builder streams
//!   events.
//! - A **log-consumer task** that receives [`LogEvent`]s and updates the
//!   spinner.
//!
//! ### `LogEvent` variants
//!
//! | Variant                      | Meaning                                           |
//! |------------------------------|---------------------------------------------------|
//! | `Line(String)`               | Update the parent spinner message.                |
//! | `ChildStart { id, label }`   | Create a sub-spinner below the parent.            |
//! | `ChildLine { id, line }`     | Update a child spinner's message.                 |
//! | `ChildFinish { id, … }`      | Close a child spinner with ✓ or ✗.                |
//!
//! The `ChildStart` / `ChildLine` / `ChildFinish` events are used only by the
//! `cargo` builder when it compiles for multiple targets in parallel (see
//! below).
//!
//! ## Inner Parallelism: `CargoBuilder`
//!
//! When a `cargo` builder lists multiple `targets`, it spawns one Tokio task
//! per target inside its own inner `JoinSet` — a second level of concurrency
//! nested inside the outer builder task.
//!
//! Each inner task:
//!
//! 1. Creates a [`tempfile::TempDir`] and passes it as `--target-dir` so the
//!    `cargo build` process does not contend with sibling builds on cargo's
//!    file lock.
//! 2. Emits a `ChildStart` event so the UI creates a dedicated sub-spinner.
//! 3. Uses `line_bridge` to adapt the plain-string stderr stream from
//!    `run_cargo_build` into `ChildLine` events on the parent [`LogSender`].
//! 4. After the build, copies artifacts to stable `target/<triple>/release/`
//!    paths before the `TempDir` is dropped.
//! 5. Emits a `ChildFinish` event when done.
//!
//! Within `run_cargo_build` itself, stderr and the JSON stdout are consumed
//! concurrently in separate `tokio::spawn` tasks so neither stream blocks the
//! other.
//!
//! ## Other Builders
//!
//! | Builder     | Async strategy                                                                  |
//! |-------------|---------------------------------------------------------------------------------|
//! | `archive`   | `tokio::task::spawn_blocking` for the CPU-bound tar walk; sends `Line` events.  |
//! | `cargo_doc` | Spawns one `tokio::spawn` to stream stderr; awaits `cargo doc` exit.            |
//! | `markdown`  | Sequential per-file render loop; `spawn_blocking` for the directory walk.       |
//! | `script`    | Runs commands sequentially; streams stdout **and** stderr in parallel tasks.    |

use miette::Result;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use std::path::PathBuf;
use tokio::sync::mpsc::UnboundedSender;

pub mod archive;
pub mod cargo;
pub mod markdown;
pub mod script;

use archive::{ArchiveBuilder, ArchiveBuilderConfig};
use cargo::{CargoBuilder, CargoBuilderConfig, CargoDocBuilder, CargoDocBuilderConfig};
use markdown::{MarkdownBuilder, MarkdownBuilderConfig};
use script::{ScriptBuilder, ScriptBuilderConfig};

/// Events emitted by builders and forwarded to the progress-bar manager in
/// [`crate::site`].
///
/// Most builders only ever send [`LogEvent::Line`].  Builders that fan out
/// into parallel sub-tasks (e.g. [`crate::builders::cargo::CargoBuilder`]
/// compiling for multiple targets simultaneously) additionally use the
/// `Child*` variants so the UI can show a dedicated spinner per sub-task.
#[derive(Debug)]
pub enum LogEvent {
    /// A plain output line from the top-level builder task.
    Line(String),
    /// Register a new child task.  The receiver will create a sub-spinner
    /// immediately below the parent spinner.
    ChildStart {
        /// Unique key used to route subsequent [`LogEvent::ChildLine`] and
        /// [`LogEvent::ChildFinish`] messages.
        id: String,
        /// Human-readable label shown in the sub-spinner's prefix.
        label: String,
    },
    /// A log line produced by a specific child task.
    ChildLine { id: String, line: String },
    /// Signal that a child task has finished.
    ChildFinish {
        id: String,
        success: bool,
        /// Short one-line summary displayed as the spinner's final message.
        summary: String,
    },
}

/// A sender used to stream [`LogEvent`]s from a builder back to the
/// progress-bar manager in [`crate::site`]. Errors sending are silently
/// ignored because the receiver may already be gone when a builder finishes.
pub type LogSender = UnboundedSender<LogEvent>;

/// A single `[[builders]]` entry: the builder itself plus optional dependency
/// metadata.
///
/// # Dependency ordering
///
/// By default every builder runs concurrently with all others.  When a builder
/// must only start *after* another one has finished successfully, give the
/// prerequisite an `id` and list that id in the dependent's `depends_on`:
///
/// ```toml
/// [[builders]]
/// type = "cargo"
/// id   = "compile"               # ← give this builder a name
///
/// [[builders]]
/// type   = "script"
/// script = ["strip target/release/my_bin"]
/// outputs = ["target/release/my_bin"]
/// depends_on = ["compile"]       # ← wait for the builder above
/// ```
///
/// Circular dependencies are detected before any builder starts and reported
/// as an error.
#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema)]
pub struct BuilderEntry {
    /// The builder's type-specific configuration (type tag + all builder
    /// fields), serialised flat into the same TOML table.
    #[serde(flatten)]
    pub builder: AnyBuilder,

    /// Optional identifier for this builder.  Other builders reference this
    /// string in their `depends_on` list.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub id: Option<String>,

    /// IDs of builders that must complete successfully before this one starts.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub depends_on: Vec<String>,
}

impl BuilderEntry {
    /// Short human-readable label forwarded from the inner builder.
    pub fn label(&self) -> &'static str {
        self.builder.label()
    }

    /// Run the inner builder, forwarding the version string and log sender.
    pub async fn build(&self, version: &str, log: LogSender) -> Result<Vec<ArtifactPath>> {
        self.builder.build(version, log).await
    }
}

#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema)]
#[serde(tag = "type", rename_all = "snake_case")]
pub enum AnyBuilder {
    /// Creates a `.tar.gz` archive of the source tree, automatically excluding
    /// files and directories matched by any `.gitignore` found in the hierarchy.
    ///
    /// ```toml
    /// [[builders]]
    /// type = "archive"
    /// source_dir = "."                      # optional, defaults to CWD
    /// output = "myproject-1.0.0.tar.gz"     # optional, defaults to source.tar.gz
    /// prefix = "myproject-1.0.0"            # optional, defaults to source_dir name
    /// ```
    Archive(ArchiveBuilderConfig),

    /// Compiles the crate in release mode with `cargo build --release`.
    /// One or more target triples can be specified for cross-compilation;
    /// omitting `targets` builds for the host platform.
    ///
    /// ```toml
    /// [[builders]]
    /// type = "cargo"
    /// targets = ["x86_64-unknown-linux-musl", "aarch64-unknown-linux-musl"]
    /// manifest_path = "Cargo.toml"          # optional
    /// ```
    Cargo(CargoBuilderConfig),

    /// Generates API documentation with `cargo doc`.
    /// Returns the per-crate doc directory (e.g. `target/doc/my_crate`) as an
    /// artifact so it can be published or archived by a later pipeline step.
    ///
    /// ```toml
    /// [[builders]]
    /// type = "cargo_doc"
    /// no_deps = true                        # optional, skip dependency docs
    /// manifest_path = "Cargo.toml"          # optional
    /// ```
    CargoDoc(CargoDocBuilderConfig),

    /// Runs an arbitrary sequence of shell commands and collects declared
    /// output paths as release artifacts.
    ///
    /// Each script line is passed to `sh -c`; the build fails immediately if
    /// any command exits with a non-zero status.
    ///
    /// ```toml
    /// [[builders]]
    /// type = "script"
    /// script = [
    ///   "make release",
    ///   "strip target/mybin",
    /// ]
    /// outputs = ["target/mybin"]
    /// ```
    Script(ScriptBuilderConfig),

    /// Renders a directory of Markdown files to standalone HTML5 documents.
    ///
    /// Every `.md` file is rendered to a mirrored `.html` file in the output
    /// directory.  Non-Markdown files referenced by local links or image
    /// embeds are copied to the output directory so that relative URLs remain
    /// valid.  Files excluded by `.gitignore` rules are automatically skipped.
    ///
    /// ```toml
    /// [[builders]]
    /// type      = "markdown"
    /// input     = "docs/"
    /// output    = "docs-html/" # optional
    /// recursive = true         # optional, default true
    /// ```
    Markdown(MarkdownBuilderConfig),
}

impl AnyBuilder {
    /// A short human-readable label used in progress-bar prefixes.
    pub fn label(&self) -> &'static str {
        match self {
            Self::Archive(_) => "archive",
            Self::Cargo(_) => "cargo-build",
            Self::CargoDoc(_) => "cargo-doc",
            Self::Markdown(_) => "markdown",
            Self::Script(_) => "script",
        }
    }

    pub async fn build(&self, version: &str, log: LogSender) -> Result<Vec<ArtifactPath>> {
        match self {
            Self::Archive(config) => ArchiveBuilder.build(config.clone(), version, log).await,
            Self::Cargo(config) => CargoBuilder.build(config.clone(), version, log).await,
            Self::CargoDoc(config) => CargoDocBuilder.build(config.clone(), version, log).await,
            Self::Markdown(config) => MarkdownBuilder.build(config.clone(), version, log).await,
            Self::Script(config) => ScriptBuilder.build(config.clone(), version, log).await,
        }
    }
}

pub struct ArtifactPath {
    pub path: PathBuf,
    pub name: String,
    /// Lowercase hexadecimal SHA1 digest of the artifact's contents, if computed.
    pub hash: Option<String>,
}

/// # Implementing a New Builder
///
/// This section walks you through adding a brand-new builder type to Abbaye,
/// from an empty file to a fully working `[[builders]]` entry that users can
/// drop into their `abbaye.toml`.
///
/// The worked example is a **`make` builder** that runs one or more `make`
/// targets and collects declared output paths as release artifacts.
///
/// ## How Builders Plug In
///
/// Every builder type is one variant of the [`AnyBuilder`] enum.  The enum
/// acts as the TOML-visible type tag (`type = "make"`) and routes calls down
/// to the concrete implementation.  The [`Builder`] trait is the interface
/// every implementation must satisfy:
///
/// ```text
/// abbaye.toml  ──►  AnyBuilder enum  ──►  BuilderEntry
///                                              │
///                                              ▼
///                                        Builder trait
///                                              │
///                                              ▼
///                                    src/builders/make.rs
/// ```
///
/// ## Step 1 — Create the builder file
///
/// Create `src/builders/make.rs`.  Start with imports that mirror what the
/// existing builders use:
///
/// ```rust,ignore
/// use std::{path::PathBuf, process::Stdio};
///
/// use miette::{IntoDiagnostic, Result, miette};
/// use schemars::JsonSchema;
/// use serde::{Deserialize, Serialize};
/// use tokio::io::{AsyncBufReadExt, BufReader};
/// use tokio::process::Command;
///
/// use crate::builders::{ArtifactPath, Builder, LogEvent, LogSender};
/// ```
///
/// | Import          | Purpose                                                           |
/// |-----------------|-------------------------------------------------------------------|
/// | `ArtifactPath`  | The return type: a path plus display name and optional hash.      |
/// | `Builder`       | The trait your struct must implement.                             |
/// | `LogEvent`      | The structured event type sent over the log channel.              |
/// | `LogSender`     | An `mpsc::UnboundedSender<LogEvent>` — your handle to the UI.     |
///
/// ## Step 2 — Write the config struct
///
/// The config struct holds every field that can appear in the TOML table.
/// It must derive exactly these traits (all are required for the builder
/// machinery):
///
/// ```rust,ignore
/// /// Configuration for [`MakeBuilder`].
/// #[derive(Debug, Default, Clone, Deserialize, Serialize, JsonSchema)]
/// pub struct MakeBuilderConfig {
///     /// `make` target to build. Defaults to the default target when absent.
///     pub target: Option<String>,
///
///     /// Path to the Makefile. Passed as `-f <path>`.
///     pub makefile: Option<PathBuf>,
///
///     /// Paths of the files produced by `make` to treat as release artifacts.
///     #[serde(default)]
///     pub outputs: Vec<PathBuf>,
/// }
/// ```
///
/// | Derive        | Why it is required                                                |
/// |---------------|-------------------------------------------------------------------|
/// | `Debug`       | Diagnostic printing.                                              |
/// | `Default`     | The [`Builder`] trait bound requires it for the associated type.  |
/// | `Clone`       | [`BuilderEntry::clone`] is used when spawning the builder task.   |
/// | `Deserialize` | Figment deserialises the TOML table into this struct.             |
/// | `Serialize`   | Needed for `abbaye init` and JSON Schema generation.              |
/// | `JsonSchema`  | Powers `abbaye dump-schema` so editors get completion/validation. |
///
/// Every public field should have a doc comment — these become the field
/// descriptions in the generated JSON Schema and appear in editor tooltips.
///
/// If `Default` cannot be derived because a field has a non-false/zero/empty
/// default (e.g. a `bool` that defaults to `true`), implement `Default`
/// manually and provide a `fn default_fieldname() -> T` free function for the
/// `#[serde(default = "...")]` attribute.  See [`crate::builders::cargo`] for
/// an example.
///
/// ## Step 3 — Implement the `Builder` trait
///
/// Define a zero-sized marker struct and implement [`Builder`] for it:
///
/// ```rust,ignore
/// pub struct MakeBuilder;
///
/// impl Builder for MakeBuilder {
///     type ConfigType = MakeBuilderConfig;
///
///     async fn build(
///         &self,
///         config: Self::ConfigType,
///         version: &str,
///         log: LogSender,
///     ) -> Result<Vec<ArtifactPath>> {
///         let mut cmd = Command::new("make");
///
///         // Always expose the version being built.
///         cmd.env("ABBAYE_BUILDING_VERSION", version);
///
///         if let Some(ref makefile) = config.makefile {
///             cmd.arg("-f").arg(makefile);
///         }
///         if let Some(ref target) = config.target {
///             cmd.arg(target);
///         }
///
///         let mut child = cmd
///             .stdout(Stdio::piped())
///             .stderr(Stdio::piped())
///             .spawn()
///             .into_diagnostic()?;
///
///         // Stream stdout and stderr concurrently so neither pipe fills up
///         // and deadlocks the child process.
///         let stdout = child.stdout.take().expect("stdout was piped");
///         let stderr = child.stderr.take().expect("stderr was piped");
///         let log_out = log.clone();
///         let log_err = log.clone();
///         let stdout_task = tokio::spawn(async move {
///             let mut lines = BufReader::new(stdout).lines();
///             while let Ok(Some(line)) = lines.next_line().await {
///                 let _ = log_out.send(LogEvent::Line(line));
///             }
///         });
///         let stderr_task = tokio::spawn(async move {
///             let mut lines = BufReader::new(stderr).lines();
///             while let Ok(Some(line)) = lines.next_line().await {
///                 let _ = log_err.send(LogEvent::Line(line));
///             }
///         });
///
///         // Drain I/O tasks *before* checking the exit code to avoid
///         // losing the last lines of output.
///         let status = child.wait().await.into_diagnostic()?;
///         let _ = tokio::join!(stdout_task, stderr_task);
///
///         if !status.success() {
///             return Err(miette!(
///                 "make failed with exit status: {}",
///                 status.code().unwrap_or(-1)
///             ));
///         }
///
///         // Collect declared outputs as artifacts.
///         let mut artifacts = Vec::new();
///         for output in &config.outputs {
///             if !output.exists() {
///                 return Err(miette!(
///                     "declared output does not exist after make: {}",
///                     output.display()
///                 ));
///             }
///             let name = output
///                 .file_name()
///                 .ok_or_else(|| miette!("output path has no file name"))?
///                 .to_string_lossy()
///                 .into_owned();
///             artifacts.push(ArtifactPath { path: output.clone(), name, hash: None });
///         }
///         Ok(artifacts)
///     }
/// }
/// ```
///
/// ### Key conventions
///
/// **Always set `ABBAYE_BUILDING_VERSION`.**  Every builder must expose the
/// version being built through this environment variable so that build scripts
/// can embed it without extra plumbing.
///
/// **Always drain I/O tasks before checking the exit status.**  If you
/// `.await` the child first, the subprocess's pipes may fill up and cause it
/// to block forever before it can exit.
///
/// **Errors from `log.send(…)` are silently ignored** (`let _ = …`).  The
/// receiver may already be gone by the time a builder finishes — that is
/// expected and harmless.
///
/// **File artifacts → `dist/`, directory artifacts → `docs/`.**  The
/// orchestrator in `site.rs` distinguishes them by `path.is_dir()`.  Return
/// a directory path only for documentation trees.
///
/// **CPU-bound or blocking I/O must use `spawn_blocking`.**  Tokio runs on a
/// small thread pool; blocking it starves other tasks.
///
/// ## Step 4 — Register in `mod.rs`
///
/// Open `src/builders/mod.rs` and make four additions.
///
/// **4a — Declare the module:**
///
/// ```rust,ignore
/// pub mod make;
/// ```
///
/// **4b — Import the types:**
///
/// ```rust,ignore
/// use make::{MakeBuilder, MakeBuilderConfig};
/// ```
///
/// **4c — Add a variant to [`AnyBuilder`]** with a doc comment containing a
/// canonical TOML usage example (this becomes the JSON Schema description):
///
/// ```rust,ignore
/// /// Runs `make [target]` and collects declared output paths as artifacts.
/// ///
/// /// ```toml
/// /// [[builders]]
/// /// type    = "make"
/// /// target  = "release"        # optional
/// /// outputs = ["dist/mybin"]
/// /// ```
/// Make(MakeBuilderConfig),
/// ```
///
/// The variant name is lowercased by `rename_all = "snake_case"`, so `Make`
/// becomes `type = "make"` in TOML.  Multi-word names use `CamelCase` in
/// Rust and become `snake_case` in TOML (e.g. `WasmPack` → `wasm_pack`).
///
/// **4d — Wire up `label()` and `build()`:**
///
/// ```rust,ignore
/// Self::Make(_) => "make",   // in label()
/// Self::Make(c) => MakeBuilder.build(c.clone(), version, log).await,  // in build()
/// ```
///
/// `label()` provides the default spinner prefix when the user hasn't given
/// the builder an `id`.  Keep it short and lowercase-kebab.
///
/// ## Step 5 — Verify
///
/// ```sh
/// cargo build
/// cargo run -- dump-schema | python3 -m json.tool | grep -A 20 '"make"'
/// ```
///
/// ## Step 6 — Use it in `abbaye.toml`
///
/// ```toml
/// [[builders]]
/// type    = "make"
/// target  = "release"
/// outputs = ["build/myprogram"]
///
/// # With dependency ordering:
/// [[builders]]
/// type       = "make"
/// id         = "make-release"
/// target     = "release"
/// outputs    = ["build/myprogram"]
///
/// [[builders]]
/// type       = "script"
/// script     = ["upx build/myprogram"]
/// outputs    = ["build/myprogram"]
/// depends_on = ["make-release"]
/// ```
///
/// ## Advanced — Parallel sub-tasks with child spinners
///
/// If your builder naturally fans out into independent sub-tasks (like the
/// `cargo` builder running one `cargo build` per target triple), you can run
/// them in parallel and give each its own sub-spinner in the UI.
///
/// The pattern is always the same:
///
/// 1. Send [`LogEvent::ChildStart`] `{ id, label }` to create the sub-spinner.
/// 2. Forward output lines as [`LogEvent::ChildLine`] `{ id, line }`.
/// 3. Send [`LogEvent::ChildFinish`] `{ id, success, summary }` to close it.
///
/// ```rust,ignore
/// join_set.spawn(async move {
///     let _ = log.send(LogEvent::ChildStart {
///         id: target.clone(),
///         label: target.clone(),
///     });
///
///     // ... do work, sending ChildLine events ...
///
///     let _ = log.send(LogEvent::ChildFinish {
///         id: target.clone(),
///         success: result.is_ok(),
///         summary: "done".to_owned(),
///     });
/// });
/// ```
///
/// The `line_bridge` helper in [`crate::builders::cargo`] is a reusable
/// pattern for adapting a plain-string sender to structured [`LogEvent`]s —
/// feel free to copy or generalise it.
///
/// ## Reviewer checklist
///
/// - Config struct derives `Debug`, `Default` (or has a manual impl),
///   `Clone`, `Deserialize`, `Serialize`, `JsonSchema`.
/// - Every public config field has a doc comment.
/// - The builder sets `ABBAYE_BUILDING_VERSION` in every subprocess
///   environment.
/// - Stdout and stderr are consumed concurrently to prevent pipe deadlocks.
/// - Log send errors are silently ignored (`let _ = log.send(…)`).
/// - Blocking I/O uses `tokio::task::spawn_blocking`.
/// - Both `label()` and `build()` arms are added to [`AnyBuilder`].
/// - `pub mod` declaration and `use` imports are present in `mod.rs`.
/// - `cargo build` succeeds with no new warnings.
/// - `abbaye dump-schema` shows the new variant and all its fields.
#[allow(async_fn_in_trait)]
pub trait Builder {
    type ConfigType: Default + for<'de> Deserialize<'de> + Clone;

    /// Run the builder and return the produced artifacts.
    ///
    /// `version` is the abbaye release version currently being built (e.g.
    /// `"1.2.3"`). Implementations that spawn subprocesses must expose it as
    /// the `ABBAYE_BUILDING_VERSION` environment variable.
    ///
    /// `log` receives one-line status/output messages from the builder's
    /// subprocesses. Lines are sent without a trailing newline.  The caller
    /// displays these in the UI (e.g. as a spinner message); errors sending
    /// are ignored because the receiver may already be closed.
    async fn build(
        &self,
        config: Self::ConfigType,
        version: &str,
        log: LogSender,
    ) -> Result<Vec<ArtifactPath>>;
}