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

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.toml

@@ -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"

README.md

@@ -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) |
 

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

@@ -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/streaming.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/channel.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/diff.rs

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

crates/zeph-core/src/lib.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-mcp/src/executor.rs

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

crates/zeph-tools/src/composite.rs

@@ -60,6 +60,7 @@ mod tests {
                 summary: "matched".to_owned(),
                 blocks_executed: 1,
                 filter_stats: None,
+                diff: None,
             }))
         }
     }
@@ -91,6 +92,7 @@ mod tests {
                 summary: "second".to_owned(),
                 blocks_executed: 1,
                 filter_stats: None,
+                diff: None,
             }))
         }
     }
@@ -167,6 +169,7 @@ mod tests {
                     summary: "file_handler".to_owned(),
                     blocks_executed: 1,
                     filter_stats: None,
+                    diff: None,
                 }))
             } else {
                 Ok(None)
@@ -190,6 +193,7 @@ mod tests {
                     summary: "shell_handler".to_owned(),
                     blocks_executed: 1,
                     filter_stats: None,
+                    diff: None,
                 }))
             } else {
                 Ok(None)

crates/zeph-tools/src/executor.rs

@@ -1,6 +1,14 @@
 use std::collections::HashMap;
 use std::fmt;
 
+/// Data for rendering file diffs in the TUI.
+#[derive(Debug, Clone)]
+pub struct DiffData {
+    pub file_path: String,
+    pub old_content: String,
+    pub new_content: String,
+}
+
 /// Structured tool invocation from LLM.
 #[derive(Debug, Clone)]
 pub struct ToolCall {
@@ -51,6 +59,7 @@ pub struct ToolOutput {
     pub summary: String,
     pub blocks_executed: u32,
     pub filter_stats: Option<FilterStats>,
+    pub diff: Option<DiffData>,
 }
 
 impl fmt::Display for ToolOutput {
@@ -98,6 +107,7 @@ pub enum ToolEvent {
         output: String,
         success: bool,
         filter_stats: Option<FilterStats>,
+        diff: Option<DiffData>,
     },
 }
 
@@ -189,6 +199,7 @@ mod tests {
             summary: "$ echo hello\nhello".to_owned(),
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         };
         assert_eq!(output.to_string(), "$ echo hello\nhello");
     }

crates/zeph-tools/src/file.rs

@@ -3,7 +3,7 @@ use std::path::{Path, PathBuf};
 
 use schemars::JsonSchema;
 
-use crate::executor::{ToolCall, ToolError, ToolExecutor, ToolOutput};
+use crate::executor::{DiffData, ToolCall, ToolError, ToolExecutor, ToolOutput};
 use crate::registry::{InvocationHint, ToolDef};
 
 // Schema-only: fields are read by schemars derive, not by Rust code directly.
@@ -144,6 +144,7 @@ impl FileExecutor {
             summary: selected.join("\n"),
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         }))
     }
 
@@ -155,6 +156,8 @@ impl FileExecutor {
         let content = param_str(params, "content")?;
         let path = self.validate_path(Path::new(&path_str))?;
 
+        let old_content = std::fs::read_to_string(&path).unwrap_or_default();
+
         if let Some(parent) = path.parent() {
             std::fs::create_dir_all(parent)?;
         }
@@ -165,6 +168,11 @@ impl FileExecutor {
             summary: format!("Wrote {} bytes to {path_str}", content.len()),
             blocks_executed: 1,
             filter_stats: None,
+            diff: Some(DiffData {
+                file_path: path_str,
+                old_content,
+                new_content: content,
+            }),
         }))
     }
 
@@ -193,6 +201,11 @@ impl FileExecutor {
             summary: format!("Edited {path_str}"),
             blocks_executed: 1,
             filter_stats: None,
+            diff: Some(DiffData {
+                file_path: path_str,
+                old_content: content,
+                new_content,
+            }),
         }))
     }
 
@@ -225,6 +238,7 @@ impl FileExecutor {
             },
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         }))
     }
 
@@ -267,6 +281,7 @@ impl FileExecutor {
             },
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         }))
     }
 }

crates/zeph-tools/src/lib.rs

@@ -19,8 +19,8 @@ pub use audit::{AuditEntry, AuditLogger, AuditResult};
 pub use composite::CompositeExecutor;
 pub use config::{AuditConfig, ScrapeConfig, ShellConfig, ToolsConfig};
 pub use executor::{
-    FilterStats, MAX_TOOL_OUTPUT_CHARS, ToolCall, ToolError, ToolEvent, ToolEventTx, ToolExecutor,
-    ToolOutput, truncate_tool_output,
+    DiffData, FilterStats, MAX_TOOL_OUTPUT_CHARS, ToolCall, ToolError, ToolEvent, ToolEventTx,
+    ToolExecutor, ToolOutput, truncate_tool_output,
 };
 pub use file::FileExecutor;
 pub use filter::{

crates/zeph-tools/src/scrape.rs

@@ -106,6 +106,7 @@ impl ToolExecutor for WebScrapeExecutor {
             summary: outputs.join("\n\n"),
             blocks_executed,
             filter_stats: None,
+            diff: None,
         }))
     }
 
@@ -134,6 +135,7 @@ impl ToolExecutor for WebScrapeExecutor {
             summary: result,
             blocks_executed: 1,
             filter_stats: None,
+            diff: None,
         }))
     }
 }

crates/zeph-tools/src/shell.rs

@@ -207,6 +207,17 @@ impl ShellExecutor {
             };
             self.log_audit(block, result, duration_ms).await;
 
+            if let Some(ref tx) = self.tool_event_tx {
+                let _ = tx.send(ToolEvent::Completed {
+                    tool_name: "bash".to_owned(),
+                    command: (*block).to_owned(),
+                    output: out.clone(),
+                    success: !out.contains("[error]"),
+                    filter_stats: None,
+                    diff: None,
+                });
+            }
+
             let sanitized = sanitize_output(&out);
             let mut per_block_stats: Option<FilterStats> = None;
             let filtered = if let Some(ref registry) = self.output_filter_registry {
@@ -252,6 +263,7 @@ impl ShellExecutor {
                     output: out.clone(),
                     success: !out.contains("[error]"),
                     filter_stats: per_block_stats,
+                    diff: None,
                 });
             }
             outputs.push(format!("$ {block}\n{filtered}"));
@@ -262,6 +274,7 @@ impl ShellExecutor {
             summary: outputs.join("\n\n"),
             blocks_executed,
             filter_stats: cumulative_filter_stats,
+            diff: None,
         }))
     }
 

crates/zeph-tools/src/trust_gate.rs

@@ -119,6 +119,7 @@ mod tests {
                 summary: "ok".into(),
                 blocks_executed: 1,
                 filter_stats: None,
+                diff: None,
             }))
         }
     }

crates/zeph-tui/Cargo.toml

@@ -12,6 +12,7 @@ crossterm.workspace = true
 pulldown-cmark.workspace = true
 ratatui.workspace = true
 thiserror.workspace = true
+similar.workspace = true
 throbber-widgets-tui = "0.10"
 tokio = { workspace = true, features = ["sync", "rt", "time"] }
 unicode-width.workspace = true