diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 33ec5c2..1988864 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,7 +28,7 @@ jobs:
         run: cargo fmt -- --check
 
       - name: Clippy
-        run: cargo clippy -- -D warnings
+        run: cargo clippy --all-features -- -D warnings
 
       - name: Tests
-        run: cargo test
+        run: cargo test --all-features
diff --git a/AGENTS.md b/AGENTS.md
index 485f26b..acb2746 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -36,7 +36,7 @@ cargo clippy -- -D warnings
 - **Scanner** (`src/scanner/`): Tree-sitter AST parsing and pattern matching across languages
 - **Rules** (`rules/`): TOML-based pattern definitions with tree-sitter queries and policy templates (Rego today)
 - **Rego** (`src/rego/`): Policy-as-Code generation from scan findings (Rego/OPA today; additional engines like Cedar planned)
-- **Output** (`src/output/`): Formatters (JSON, text; SARIF planned)
+- **Output** (`src/output/`): Formatters (JSON, text)
 
 ### Design principles
 
diff --git a/Cargo.toml b/Cargo.toml
index d0f8720..1e7e60f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,6 +12,11 @@ readme = "README.md"
 keywords = ["authorization", "policy-as-code", "opa", "rego", "static-analysis"]
 categories = ["command-line-utilities", "development-tools"]
 
+[features]
+# Exposes internal implementation modules (config, deep, mcp, output, scanner)
+# as public API. No semver stability guarantee; opt in explicitly.
+unstable = []
+
 [dependencies]
 clap = { version = "4", features = ["derive", "env"] }
 serde = { version = "1", features = ["derive"] }
@@ -41,6 +46,26 @@ libc = "0.2"
 tempfile = "3"
 mockito = "1"
 
+# Integration tests in `tests/` reach into modules gated behind `unstable`
+# (deep, mcp, scanner, config). Mark them as requiring the feature so
+# default `cargo test` skips them cleanly; CI runs `cargo test --features
+# unstable` to exercise them.
+[[test]]
+name = "deep_http_integration"
+required-features = ["unstable"]
+
+[[test]]
+name = "deep_subprocess_integration"
+required-features = ["unstable"]
+
+[[test]]
+name = "mcp_stdio_integration"
+required-features = ["unstable"]
+
+[[test]]
+name = "scanner_enforcement_points"
+required-features = ["unstable"]
+
 [package.metadata.binstall]
 pkg-url = "{ repo }/releases/download/v{ version }/zift-{ target }{ archive-suffix }"
 bin-dir = "{ bin }{ binary-ext }"
diff --git a/docs/DESIGN.md b/docs/DESIGN.md
index 40815e5..dcc5dcd 100644
--- a/docs/DESIGN.md
+++ b/docs/DESIGN.md
@@ -254,7 +254,7 @@ SCAN OPTIONS:
     --category, -c      Filter to specific auth category(s)
     --confidence        Minimum confidence level (high|medium|low)
     --exclude, -e       Glob patterns to exclude
-    --format, -f        Output format (text|json|sarif)
+    --format, -f        Output format (text|json)
     --output, -o        Write findings to file (default: stdout)
     --rules-dir         Additional pattern rules directory
     --config            Path to config file (default: .zift.toml)
@@ -344,7 +344,7 @@ additional = ["./custom-rules"]
 - Integration with findings pipeline
 
 ### Phase 5: CI integration + SARIF (3-5 days)
-- SARIF output format (for GitHub Code Scanning, VS Code)
+- SARIF output format (for GitHub Code Scanning, VS Code) — planned for v0.2
 - Exit codes for CI (findings above threshold → non-zero)
 - Baseline/diff mode (only report new findings since last scan)
 - GitHub Actions example workflow
diff --git a/src/cli.rs b/src/cli.rs
index 648ac9e..a23c8a9 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -217,7 +217,6 @@ pub enum OutputFormat {
     #[default]
     Text,
     Json,
-    Sarif,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, ValueEnum)]
diff --git a/src/commands/scan.rs b/src/commands/scan.rs
index 14d3af0..182630c 100644
--- a/src/commands/scan.rs
+++ b/src/commands/scan.rs
@@ -7,12 +7,6 @@ use crate::rules;
 use crate::scanner;
 
 pub fn execute(args: ScanArgs, config: ZiftConfig) -> Result<()> {
-    if matches!(args.format, OutputFormat::Sarif) {
-        return Err(ZiftError::General(
-            "SARIF output not yet implemented".into(),
-        ));
-    }
-
     let path = args.path.canonicalize().map_err(|e| {
         ZiftError::General(format!(
             "failed to resolve path '{}': {e}",
@@ -85,7 +79,6 @@ pub fn execute(args: ScanArgs, config: ZiftConfig) -> Result<()> {
             result.enforcement_points,
             &mut writer,
         )?,
-        OutputFormat::Sarif => unreachable!("pre-checked above"),
     }
 
     Ok(())
diff --git a/src/deep/candidate.rs b/src/deep/candidate.rs
index 26ded77..4579050 100644
--- a/src/deep/candidate.rs
+++ b/src/deep/candidate.rs
@@ -118,6 +118,7 @@ pub enum CandidateKind {
 }
 
 #[derive(Debug, Clone)]
+#[allow(dead_code)] // `kind`/`seed_category` are read in tests + Debug output
 pub struct Candidate {
     pub kind: CandidateKind,
     /// Path relative to scan root.
diff --git a/src/error.rs b/src/error.rs
index c8ac6dc..a23c15a 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -3,6 +3,7 @@ use std::path::PathBuf;
 use thiserror::Error;
 
 use crate::deep::error::DeepError;
+use crate::types::Language;
 
 pub type Result<T> = std::result::Result<T, ZiftError>;
 
@@ -26,6 +27,9 @@ pub enum ZiftError {
     #[error("deep scan: {0}")]
     Deep(#[from] DeepError),
 
+    #[error("{0} is not yet supported; see the README for the current language matrix")]
+    UnsupportedLanguage(Language),
+
     #[error("{0}")]
     General(String),
 }
diff --git a/src/lib.rs b/src/lib.rs
index d6576c8..09c2414 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,18 +1,63 @@
 //! Zift — static analysis for embedded authorization logic.
 //!
-//! This crate is published as both a binary (`zift`) and a library. The
-//! binary at `src/main.rs` is a thin shim over the library; downstream
-//! consumers (e.g. the MCP server in PR 2) can depend on the library.
+//! This crate is published as both a binary (`zift`) and a library.
+//!
+//! # Stable public API
+//!
+//! The types below form the semver-committed surface. Everything else is
+//! internal or opt-in via `--features unstable`.
+//!
+//! - [`cli`] — CLI argument types (`Cli`, `ScanArgs`, …)
+//! - [`error`] — `ZiftError` and `Result<T>`
+//! - [`types`] — core data types (`Finding`, `Language`, `AuthCategory`, …)
+//! - [`rules`] — rule loading (read-only)
+//! - [`rego`] — policy generation; `rego::validator` is the stable surface
+//! - [`run`] — binary entry point
 
+// Stable public API
 pub mod cli;
-pub mod commands;
+pub mod error;
+pub mod rego;
+pub mod rules;
+pub mod types;
+
+// Internal implementation — not accessible to downstream crates; the binary
+// reaches these only through `run()` below.
+mod commands;
+mod logging;
+
+// Internal modules exposed conditionally when the `unstable` feature is
+// enabled. Within this crate they are always reachable via `crate::…`.
+#[cfg(feature = "unstable")]
 pub mod config;
+#[cfg(not(feature = "unstable"))]
+mod config;
+
+#[cfg(feature = "unstable")]
 pub mod deep;
-pub mod error;
-pub mod logging;
+#[cfg(not(feature = "unstable"))]
+mod deep;
+
+#[cfg(feature = "unstable")]
 pub mod mcp;
+#[cfg(not(feature = "unstable"))]
+mod mcp;
+
+#[cfg(feature = "unstable")]
 pub mod output;
-pub mod rego;
-pub mod rules;
+#[cfg(not(feature = "unstable"))]
+mod output;
+
+#[cfg(feature = "unstable")]
 pub mod scanner;
-pub mod types;
+#[cfg(not(feature = "unstable"))]
+mod scanner;
+
+/// Entry point used by the `zift` binary.
+///
+/// Initialises logging, loads config, and dispatches the CLI command.
+pub fn run(cli: cli::Cli) -> error::Result<()> {
+    logging::init(cli.verbose);
+    let cfg = config::load_config(&cli.config)?;
+    commands::dispatch(cli, cfg)
+}
diff --git a/src/main.rs b/src/main.rs
index 2dfb69d..59bb3a0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,19 +1,10 @@
 use clap::Parser;
 
 use zift::cli::Cli;
-use zift::{commands, config, error, logging};
 
 fn main() {
-    let cli = Cli::parse();
-    logging::init(cli.verbose);
-
-    if let Err(e) = run(cli) {
+    if let Err(e) = zift::run(Cli::parse()) {
         eprintln!("Error: {e}");
         std::process::exit(1);
     }
 }
-
-fn run(cli: Cli) -> error::Result<()> {
-    let config = config::load_config(&cli.config)?;
-    commands::dispatch(cli, config)
-}
diff --git a/src/mcp/jsonrpc.rs b/src/mcp/jsonrpc.rs
index 08c0403..d701150 100644
--- a/src/mcp/jsonrpc.rs
+++ b/src/mcp/jsonrpc.rs
@@ -9,6 +9,7 @@ use serde_json::Value;
 use std::io::{BufRead, Write};
 
 /// Standard JSON-RPC 2.0 error codes (-32700 … -32600 reserved).
+#[allow(dead_code)] // full set kept for protocol completeness
 pub mod error_code {
     pub const PARSE_ERROR: i32 = -32700;
     pub const INVALID_REQUEST: i32 = -32600;
@@ -120,6 +121,7 @@ pub fn write_response<W: Write>(writer: &mut W, resp: &Response) -> std::io::Res
 }
 
 #[derive(Debug)]
+#[allow(dead_code)] // `raw` retained for Debug-trace diagnostics
 pub enum FrameError {
     Io(std::io::Error),
     Parse { message: String, raw: String },
diff --git a/src/mcp/server.rs b/src/mcp/server.rs
index 28e4587..abbdc0e 100644
--- a/src/mcp/server.rs
+++ b/src/mcp/server.rs
@@ -135,6 +135,7 @@ pub fn handle_request(ctx: &ServerContext, req: &Request, id: Value) -> Response
 /// Errors a handler can return at the JSON-RPC layer (distinct from tool
 /// errors, which are surfaced inside a `tools/call` result with `isError: true`).
 #[derive(Debug)]
+#[allow(dead_code)] // `Internal` matched in dispatch; reserved for future handlers
 pub enum HandlerError {
     InvalidParams(String),
     Internal(String),
diff --git a/src/scanner/parser.rs b/src/scanner/parser.rs
index ec9fb72..963b508 100644
--- a/src/scanner/parser.rs
+++ b/src/scanner/parser.rs
@@ -16,9 +16,7 @@ pub fn get_language(lang: Language, is_tsx_jsx: bool) -> Result<tree_sitter::Lan
         (Language::Java, _) => Ok(tree_sitter_java::LANGUAGE.into()),
         (Language::Python, _) => Ok(tree_sitter_python::LANGUAGE.into()),
         (Language::Go, _) => Ok(tree_sitter_go::LANGUAGE.into()),
-        _ => Err(ZiftError::General(format!(
-            "language {lang:?} not yet supported"
-        ))),
+        _ => Err(ZiftError::UnsupportedLanguage(lang)),
     }
 }
 
@@ -41,6 +39,7 @@ pub fn parse_source(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::error::ZiftError;
 
     #[test]
     fn parse_typescript() {
@@ -110,7 +109,11 @@ mod tests {
         // C# has no structural grammar wired up yet — kept as the canary
         // that `unsupported_language_returns_error` keeps testing what its
         // name says it does. (Was Go before v0.2 added Go support.)
-        assert!(get_language(Language::CSharp, false).is_err());
+        let err = get_language(Language::CSharp, false).unwrap_err();
+        assert!(matches!(
+            err,
+            ZiftError::UnsupportedLanguage(Language::CSharp)
+        ));
         assert!(!is_language_supported(Language::CSharp));
     }
 }