Merge pull request #497 from euisuh/fix/mcp-batch-limit-460

fix(mcp): reject oversized batches before execution

ROADMAP.md

@@ -2,7 +2,7 @@
 
 **Stage: pre-alpha** · next: alpha, ~5% and ~110–180 h away (the alpha gate's three failing workflows)
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-10 · **Change:** minor (readiness by audience with hours to ~95 %) · **Target:** Avid Pro Tools Ultimate 2026.4.1
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-14 · **Change:** trivial (MCP batch limit validation) · **Target:** Avid Pro Tools Ultimate 2026.4.1
 
 SoundCraft is a clean-room, pure-Rust digital audio workstation that aims at full parity with
 Avid Pro Tools, and then beyond it: faster, open, scriptable and agent-controllable. This page is
@@ -122,6 +122,7 @@ mutated and truncated movies. Field reports from the first public week are track
 
 ## Progress log
 
+- **2026-10-14:** MCP `batch` rejects more than 1000 calls before executing any command, instead of silently running only the first 1000 (#460). No readiness percentage change.
 - **2026-10-13:** `mix.instrument` takes the built-in instrument's parameters in `params` (validated, clamped) and refuses any other field, so a synth setting written beside `plugin` is an error instead of being accepted and ignored (#265)
 - **2026-10-13:** A bounce of a bus that an aux returns onto lines up with the timeline: the aux insert's lookahead is compensated like the main mix's (it left the bus late and cut the end off), and tracks routed to that bus wait for it too (#246)
 - **2026-10-13:** Delay compensation covers the inserts of the master faders: a bounce of the main mix with a Maximizer on the master lines up with the same mix without it (it came out 71 samples late) (#351)
@@ -155,6 +156,7 @@ mutated and truncated movies. Field reports from the first public week are track
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-14 | trivial | Progress log: oversized MCP batches rejected before execution (#460) |
 | 2026-10-13 | trivial | Progress log: mix.instrument params, unknown fields refused (#265) |
 | 2026-10-13 | trivial | Progress log: bus bounce compensates aux returns (#246) |
 | 2026-10-13 | trivial | Progress log: master insert latency compensated (#351) |

crates/automation/src/mcp.rs

@@ -6,6 +6,7 @@ use std::io::{BufRead, Write};
 
 pub const PROTOCOL_VERSION: &str = "2025-06-18";
 const SUPPORTED: &[&str] = &["2025-06-18", "2025-03-26", "2024-11-05"];
+const MAX_BATCH_CALLS: usize = 1000;
 
 const INSTRUCTIONS: &str = "SoundCraft is a digital audio workstation (Pro Tools-class). Everything a user can do is a \
 command: call `list_commands` to discover ids and their params, then `execute` (or `batch`). Positions are samples \
@@ -37,8 +38,8 @@ pub fn tool_definitions() -> Vec<Value> {
         ),
         tool(
             "batch",
-            "Run several commands in order; stops at the first error unless keep_going.",
-            json!({"calls": {"type": "array", "items": {"type": "object", "properties": {"command": {"type": "string"}, "params": {"type": "object"}}}}, "keep_going": {"type": "boolean"}}),
+            "Run up to 1000 commands in order; stops at the first error unless keep_going. Larger batches are rejected before any command runs.",
+            json!({"calls": {"type": "array", "maxItems": MAX_BATCH_CALLS, "items": {"type": "object", "properties": {"command": {"type": "string"}, "params": {"type": "object"}}}}, "keep_going": {"type": "boolean"}}),
             &["calls"],
         ),
         tool(
@@ -135,9 +136,12 @@ impl<B: Backend> Server<B> {
                 let Some(calls) = args.get("calls").and_then(Value::as_array) else {
                     return error_result("`calls` must be an array");
                 };
+                if calls.len() > MAX_BATCH_CALLS {
+                    return error_result(&format!("`calls` must contain at most {MAX_BATCH_CALLS} commands; no commands were executed"));
+                }
                 let mut out = Vec::new();
                 let mut failed = false;
-                for c in calls.iter().take(1000) {
+                for c in calls {
                     let Some(cmd) = c.get("command").and_then(Value::as_str).map(str::trim).filter(|s| !s.is_empty()) else {
                         out.push(json!({"command": "", "ok": false, "error": "`command` required"}));
                         failed = true;

crates/automation/tests/agent_tasks.rs

@@ -31,6 +31,8 @@ fn handshake_and_tool_list() {
     assert_eq!(r["result"]["serverInfo"]["name"], "soundcraft");
     let r = rpc(&mut s, 2, "tools/list", json!({}));
     assert!(r["result"]["tools"].as_array().unwrap().len() >= 10);
+    let batch = r["result"]["tools"].as_array().unwrap().iter().find(|tool| tool["name"] == "batch").unwrap();
+    assert_eq!(batch["inputSchema"]["properties"]["calls"]["maxItems"], 1000);
     assert!(s.handle(&json!({"jsonrpc": "2.0", "method": "notifications/initialized"})).is_none());
     let r = rpc(&mut s, 3, "nope", json!({}));
     assert_eq!(r["error"]["code"], -32601);
@@ -171,3 +173,35 @@ fn batch_rejects_non_array_calls() {
     assert!(text.contains("`calls` must be an array"), "{text}");
     assert_eq!(session(&mut s)["tracks"].as_array().unwrap().len(), 0);
 }
+
+#[test]
+fn batch_rejects_oversize_calls_before_any_mutation() {
+    for keep_going in [false, true] {
+        let mut s = Server::new(Headless::new(Engine::default()));
+        let before = session(&mut s);
+        let mut calls = vec![json!({"command": "engine.history"}); 1001];
+        calls[0] = json!({"command": "track.new", "params": {"name": "Must not be created"}});
+        let r = rpc(&mut s, 1, "tools/call", json!({"name": "batch", "arguments": {"calls": calls, "keep_going": keep_going}}));
+        assert_eq!(session(&mut s), before, "oversize batch mutated the session (keep_going={keep_going})");
+        assert!(s.backend.engine.journal.is_empty());
+        assert!(!s.backend.engine.can_undo());
+        assert_eq!(r["result"]["isError"], true);
+        let text = r["result"]["content"][0]["text"].as_str().unwrap();
+        assert!(text.contains("1000"), "{text}");
+    }
+}
+
+#[test]
+fn batch_accepts_empty_and_limit_sized_calls_in_order() {
+    for count in [0, 1000] {
+        let mut s = Server::new(Headless::new(Engine::default()));
+        let calls: Vec<_> = (0..count).map(|at| json!({"command": "session.format_time", "params": {"at": at, "format": "samples"}})).collect();
+        let results = tool(&mut s, "batch", json!({"calls": calls}));
+        let results = results.as_array().unwrap();
+        assert_eq!(results.len(), count);
+        for (at, result) in results.iter().enumerate() {
+            assert_eq!(result["ok"], true);
+            assert_eq!(result["result"]["text"], at.to_string());
+        }
+    }
+}

docs/mcp.md

@@ -90,7 +90,7 @@ files it was given rather than guarding against other software on the computer.
 |---|---|
 | `list_commands` | Discover every command (id, label, menu path, shortcut, params doc, enabled). |
 | `execute` | Run one command with JSON params. |
-| `batch` | Run several commands in order (`keep_going` optional). Any failed call makes the tool result `isError: true`; with `keep_going` the remaining calls still run and every result is listed. |
+| `batch` | Run up to 1000 commands in order (`keep_going` optional). Larger batches return `isError: true` before executing any command. Any failed call makes the tool result `isError: true`; with `keep_going` the remaining calls still run and every result is listed. |
 | `inspect_session` | Verify work: tracks, clips, mixer, plugins, sends, automation, markers, selection; each `sources[]` entry includes `loaded` (decoded audio in the pool). |
 | `new_session`, `open_session`, `save_session` | Session files (`.scraft`, audio in `Audio Files/`). `open_session` returns `missing`: the media files that could not be loaded (empty when all are found). `save_session` won't save over another existing file unless `replace` is true. |
 | `import_audio` | WAV, AIFF, FLAC, MP3, OGG, AAC/M4A, ALAC, CAF onto a new or existing track. |

docs/roadmap.md

@@ -1,6 +1,6 @@
 # SoundCraft roadmap: milestones and what's next
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-10 · **Change:** minor (alpha gate added; stage re-normalized to pre-alpha) · **Target:** Avid Pro Tools Ultimate 2026.4.1
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-14 · **Change:** trivial (M8 batch limit validation) · **Target:** Avid Pro Tools Ultimate 2026.4.1
 
 Forward-looking plan. Status and numbers: [`../ROADMAP.md`](../ROADMAP.md) and
 [`target-app-parity.md`](target-app-parity.md); the ranked work list: [`gaps.md`](gaps.md).
@@ -54,6 +54,9 @@ Status: ✅ done · 🟡 in progress · ⬜ not started.
 | M16 | Built-in plugin depth, sidechain, ARA | ⬜ | 110–170 |
 | M17 | Immersive delivery (ADM BWF, object renderer, binaural) and video depth | ⬜ | 80–130 |
 
+M8 follow-up (2026-10-14): MCP batches above 1000 calls are rejected before execution (#460).
+The limit is advertised in the tool schema and description; stage and readiness estimates are unchanged.
+
 ## To beta (~350–570 h, about 60–70 % parallelizable)
 
 Beta needs ~75 % ready for real work and no blocking gap in session interchange.
@@ -86,5 +89,6 @@ There is no `cargo xtask scorecard` in this repo; the measured number is `cargo
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-14 | trivial | M8: reject oversized MCP batches before execution (#460) |
 | 2026-10-10 | minor | Added the alpha gate (3 of 6 core workflows fail → pre-alpha) |
 | 2026-10-10 | major | Created from ROADMAP.md's milestones and alpha list; added M12–M17 and the beta plan with estimates |