TUI: syntax-highlighted diff view for write/edit tool output (#455)

* feat: syntax-highlighted diff view for write/edit tool output in TUI

Add diff rendering to TUI chat panel for write and edit tool results.
FileExecutor captures old content before modifications, propagates
DiffData through agent events to TUI where it renders with green/red
backgrounds for added/removed lines, word-level change highlighting,
and syntax coloring via tree-sitter. Compact/expanded toggle reuses
existing 'e' key binding.

Closes #451

* docs: update documentation, changelog, and readme for TUI diff view

Author: bug-ops

CHANGELOG.md

@@ -7,6 +7,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 ## [Unreleased]
 
 ### Added
+- Syntax-highlighted diff view for write/edit tool output in TUI (#451)
+  - Diff rendering with green/red backgrounds for added/removed lines
+  - Word-level change highlighting within modified lines
+  - Syntax highlighting via tree-sitter
+  - Compact/expanded toggle with existing 'e' key binding
+  - New dependency: `similar` 2.7.0
 - Per-tool inline filter stats in CLI chat: `[shell] cargo test (342 lines -> 28 lines, 91.8% filtered)` (#449)
 - Filter metrics in TUI Resources panel: confidence distribution, command hit rate, token savings (#448)
 - Periodic 250ms tick in TUI event loop for real-time metrics refresh (#447)

Cargo.lock

@@ -40,6 +40,7 @@ rmcp = "0.15"
 scrape-core = "0.2.2"
 subtle = "2.6"
 schemars = "1.2"
+similar = "2.7"
 serde = "1.0"
 serde_json = "1.0"
 serial_test = "3.3"

Cargo.toml

@@ -118,7 +118,7 @@ cargo build --release --features tui
 | **Skill Trust & Quarantine** | 4-tier trust model (Trusted/Verified/Quarantined/Blocked) with blake3 integrity verification, anomaly detection with automatic blocking, and restricted tool access for untrusted skills | |
 | **Prompt Caching** | Automatic prompt caching for Anthropic and OpenAI providers, reducing latency and cost on repeated context | |
 | **Graceful Shutdown** | Ctrl-C triggers ordered teardown with MCP server cleanup and pending task draining | |
-| **TUI Dashboard** | ratatui terminal UI with tree-sitter syntax highlighting, markdown rendering, deferred model warmup, scrollbar, mouse scroll, thinking blocks, conversation history, splash screen, live metrics (including filter savings), message queueing (max 10, FIFO with Ctrl+K clear) | [TUI](https://bug-ops.github.io/zeph/guide/tui.html) |
+| **TUI Dashboard** | ratatui terminal UI with tree-sitter syntax highlighting, markdown rendering, syntax-highlighted diff view for write/edit tool output (compact/expanded toggle), deferred model warmup, scrollbar, mouse scroll, thinking blocks, conversation history, splash screen, live metrics (including filter savings), message queueing (max 10, FIFO with Ctrl+K clear) | [TUI](https://bug-ops.github.io/zeph/guide/tui.html) |
 | **Multi-Channel I/O** | CLI, Discord, Slack, Telegram, and TUI with streaming support | [Channels](https://bug-ops.github.io/zeph/guide/channels.html) |
 | **Defense-in-Depth** | Shell sandbox with relative path traversal detection, file sandbox, command filter, secret redaction (Google/GitLab patterns), audit log, SSRF protection (agent + MCP), rate limiter TTL eviction, doom-loop detection, skill trust quarantine | [Security](https://bug-ops.github.io/zeph/security.html) |
 

README.md

@@ -1158,6 +1158,7 @@ pub(super) mod agent_tests {
             summary: "tool executed successfully".to_string(),
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         }))]);
 
         let agent_channel = MockChannel::new(vec!["execute tool".to_string()]);
@@ -1356,6 +1357,7 @@ pub(super) mod agent_tests {
                 summary: "[error] command failed [exit code 1]".to_string(),
                 blocks_executed: 1,
                 filter_stats: None,
+                diff: None,
             })),
             Ok(None),
         ]);
@@ -1376,6 +1378,7 @@ pub(super) mod agent_tests {
             summary: "   ".to_string(),
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         }))]);
 
         let mut agent = Agent::new(provider, channel, registry, None, 5, executor);
@@ -1468,6 +1471,7 @@ pub(super) mod agent_tests {
                 summary: "step 1 complete".to_string(),
                 blocks_executed: 1,
                 filter_stats: None,
+                diff: None,
             })),
             Ok(None),
         ]);
@@ -1496,6 +1500,7 @@ pub(super) mod agent_tests {
                 summary: "continuing".to_string(),
                 blocks_executed: 1,
                 filter_stats: None,
+                diff: None,
             })));
         }
         let executor = MockToolExecutor::new(outputs);

crates/zeph-core/src/agent/mod.rs

@@ -619,7 +619,12 @@ impl<C: Channel, T: ToolExecutor> Agent<C, T> {
                 .instrument(tracing::info_span!("tool_exec", tool_name = %tc.name))
                 .await;
             let (output, is_error) = match tool_result {
-                Ok(Some(out)) => (out.summary, false),
+                Ok(Some(out)) => {
+                    if let Some(diff) = out.diff {
+                        let _ = self.channel.send_diff(diff).await;
+                    }
+                    (out.summary, false)
+                }
                 Ok(None) => ("(no output)".to_owned(), false),
                 Err(e) => (format!("[error] {e}"), true),
             };

crates/zeph-core/src/agent/streaming.rs

@@ -93,6 +93,18 @@ pub trait Channel: Send {
         async { Ok(()) }
     }
 
+    /// Send diff data for a tool result. No-op by default (TUI overrides).
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the underlying I/O fails.
+    fn send_diff(
+        &mut self,
+        _diff: crate::DiffData,
+    ) -> impl Future<Output = Result<(), ChannelError>> + Send {
+        async { Ok(()) }
+    }
+
     /// Request user confirmation for a destructive action. Returns `true` if confirmed.
     /// Default: auto-confirm (for headless/test scenarios).
     ///

crates/zeph-core/src/channel.rs

@@ -0,0 +1 @@
+pub use zeph_tools::executor::DiffData;

crates/zeph-core/src/diff.rs

@@ -15,7 +15,10 @@ pub mod project;
 pub mod redact;
 pub mod vault;
 
+pub mod diff;
+
 pub use agent::Agent;
 pub use agent::error::AgentError;
 pub use channel::{Channel, ChannelError, ChannelMessage};
 pub use config::Config;
+pub use diff::DiffData;

crates/zeph-core/src/lib.rs

@@ -68,6 +68,7 @@ impl ToolExecutor for McpToolExecutor {
             summary: outputs.join("\n\n"),
             blocks_executed,
             filter_stats: None,
+            diff: None,
         }))
     }
 }