fix(sed): GNU-align the stream editor and add the missing commands

crates/bashkit/docs/compatibility.md

@@ -72,7 +72,7 @@ for sandbox security reasons. See the compliance spec for details.
 | `times` | - | POSIX display process times |
 | `grep` | `-i`, `-v`, `-c`, `-n`, `-E`, `-q` | Pattern matching |
 | `rg` | `-i/-S/-s`, `-n/-N`, `--column`, `-b/--byte-offset`, `--vimgrep`, basic `--json`, `--stats`, `--null`, `-c`, `--count-matches`, `--include-zero`, `-l`, `--files-with-matches`, `--files-without-match`, `--files`, `-F`, `-w`, `-x`, `-a/--text`, `--binary`, `-m`, `-M/--max-columns`, `--max-columns-preview`, `--max-depth`, `-A`, `-B`, `-C`, separator flags, `--heading/--no-heading`, `--sort/--sortr`, `--path-separator`, `-g/--glob`, `--ignore-file`, `.ignore`/`.gitignore`, `--no-ignore*`, `--require-git/--no-require-git`, `-u/--unrestricted`, `--messages/--no-messages`, `-t/--type`, `-T/--type-not`, `--type-add`, `--type-clear`, `--type-list`, `--hidden/--no-hidden`, `-o`, `-q`, `-e`, `-f`, `-E/--encoding` (`auto`, `none`, UTF-8, UTF-16LE/BE), `-r`, `--passthru`, `--trim`, `-H/-I`, `--no-config`, `--line-buffered`, `--block-buffered`, `--mmap/--no-mmap`, `-P/--pcre2`, `--no-pcre2`, `--engine`, `--auto-hybrid-regex`, `--no-auto-hybrid-regex`, `--help`, `--version` | Recursive ripgrep-style search |
-| `sed` | `s///[g]`, `d`, `p`, `q`, `a`, `i`, `c`, `h/H/g/G/x`, `-E`, `-n`, `!` | Stream editing |
+| `sed` | `s///[gpiImMN w]`, `y`, `d`, `D`, `p`, `P`, `n`, `N`, `q[N]`, `Q[N]`, `=`, `l[N]`, `z`, `F`, `a`, `i`, `c`, `r`, `R`, `w`, `W`, `h/H/g/G/x`, `b`/`t`/`T`/`:label`, `{}`, `#`/`#n`; addresses `N`, `$`, `/re/[IM]`, `\cREc`, `first~step`, `a,b`, `a,+N`, `a,~N`, `0,/re/`, `!`; options `-n -e -f -i[SUF] -E/-r -s -z -l N -u --` and long forms | Stream editing; one stream across operands unless `-s`/`-i` |
 | `awk` | `'{print}'`, `-F`, `-v`, loops, arrays, increment, ternary | Text processing |
 | `jq` | `.field`, `.[n]`, pipes, file args, `-r`, `-c`, `-n`, `-s`, `-S`, `-e`, `-j`, `--tab`, `--arg`, `--argjson`, `-V`, combined flags | JSON processing |
 | `sleep` | `N`, `N.N` | Pause execution (max 60s) |
@@ -502,6 +502,11 @@ Identified from eval analysis, all items now implemented:
 - [x] `sed` `0~2` step addressing, even/odd line processing
 - [x] `sed` `Q` quiet quit command
 - [x] `sed` `0,/pattern/` first match addressing
+- [x] `sed` GNU rewrite, issue #2427: literal `$` in the replacement, BRE/ERE
+  translation shared by `s///` and address regexes, stateful range addresses,
+  single-stream multi-file input, preserved missing final newline, `s///Ng`,
+  the `y = l n N P D T z F r R w W` commands, `#` comments and `#n`, atomic
+  mode-preserving `-i`, and full getopt-style option parsing
 - [x] AWK `$0` modification with field re-splitting
 
 ### Not Planned

crates/bashkit/docs/threat-model.md

@@ -883,7 +883,7 @@ builtin silently fails.
 | Threat | Attack Example | Mitigation | Status |
 |--------|---------------|------------|--------|
 | Awk byte-boundary panic (TM-UNI-001) | Multi-byte chars in awk input | `catch_unwind` catches panic | PARTIAL |
-| Sed byte-boundary panic (TM-UNI-002) | Box-drawing chars in sed pattern | `catch_unwind` catches panic | PARTIAL |
+| Sed byte-boundary panic (TM-UNI-002) | Multi-byte `s` delimiter, e.g. `sed 's≠a≠X≠'` | Char-based script parser; no byte slicing of script text | FIXED |
 | Expr substr panic (TM-UNI-015) | `expr substr "café" 4 1` | `catch_unwind` catches panic | PARTIAL |
 | Printf precision panic (TM-UNI-016) | `printf "%.1s" "é"` | `catch_unwind` catches panic | PARTIAL |
 | Cut/tr byte-level parsing (TM-UNI-017) | `tr 'é' 'e'`, multi-byte in char set | `catch_unwind` catches; silent data loss | PARTIAL |

crates/bashkit/fuzz/fuzz_targets/sed_fuzz.rs

@@ -90,6 +90,22 @@ fuzz_target!(|data: &[u8]| {
                 expr.replace('\'', "'\\''"),
             );
             bashkit::testing::fuzz_exec(&mut bash, &script3, "sed_fuzz", &[]).await;
+
+            // Test 4: seeds that historically panicked or diverged (issue #2427):
+            // multi-byte `s` delimiters (TM-UNI-002), truncated scripts, and
+            // option clustering.
+            for seed in [
+                "s≠a≠X≠",
+                "s😀a😀X😀g",
+                "y≠a≠b≠",
+                "s/a",
+                "s/[//",
+                ":a;ba",
+                "b missing",
+            ] {
+                let script = format!("echo 'a' | sed '{seed}'");
+                bashkit::testing::fuzz_exec(&mut bash, &script, "sed_fuzz_seed", &[]).await;
+            }
         });
     }
 });

crates/bashkit/src/builtins/atomic_write.rs

@@ -0,0 +1,92 @@
+//! Shared atomic in-place file replacement for builtins that rewrite files.
+//!
+//! THREAT[TM-FS-016]: write a sibling temporary file, copy the original mode
+//! onto it, and rename only after the new content is fully written. Any failure
+//! leaves the source file untouched and removes the temporary.
+//!
+//! Extracted from `yq` so `sed -i` gets the same guarantees (issue #2427,
+//! finding E): the previous `sed -i` wrote straight through
+//! `FileSystem::write_file`, which recreates the entry with mode 0644 and loses
+//! the original content if the write fails part-way.
+
+use std::path::Path;
+
+use crate::fs::vfs_join;
+
+/// Failpoint names for one call site. Each builtin supplies its own so the
+/// security failpoint suite can target them independently.
+#[cfg_attr(not(feature = "failpoints"), allow(dead_code))]
+pub(crate) struct AtomicFailpoints {
+    pub(crate) allocate: &'static str,
+    pub(crate) chmod: &'static str,
+    pub(crate) rename: &'static str,
+}
+
+pub(crate) async fn atomic_replace(
+    fs: &dyn crate::fs::FileSystem,
+    target: &Path,
+    content: &[u8],
+    tool: &str,
+    failpoints: AtomicFailpoints,
+) -> std::result::Result<(), String> {
+    let parent = target.parent().unwrap_or_else(|| Path::new("/"));
+    #[cfg(feature = "failpoints")]
+    if injected_failure(failpoints.allocate, "exhausted") {
+        return Err("cannot allocate temporary file".to_string());
+    }
+    let mut temp = None;
+    for _ in 0..16 {
+        let mut suffix = [0u8; 8];
+        getrandom::fill(&mut suffix)
+            .map_err(|_| "cannot generate temporary filename".to_string())?;
+        let suffix = suffix
+            .iter()
+            .map(|byte| format!("{byte:02x}"))
+            .collect::<String>();
+        let candidate = vfs_join(parent, format!(".bashkit-{tool}-{suffix}.tmp"));
+        if !fs
+            .exists(&candidate)
+            .await
+            .map_err(|error| error.to_string())?
+        {
+            temp = Some(candidate);
+            break;
+        }
+    }
+    let temp = temp.ok_or_else(|| "cannot allocate temporary file".to_string())?;
+    if let Err(error) = fs.write_file(&temp, content).await {
+        let _ = fs.remove(&temp, false).await;
+        return Err(format!("cannot write temporary file: {error}"));
+    }
+    #[cfg(feature = "failpoints")]
+    if injected_failure(failpoints.chmod, "error") {
+        let _ = fs.remove(&temp, false).await;
+        return Err("cannot preserve file mode: injected failure".to_string());
+    }
+    if let Ok(metadata) = fs.stat(target).await
+        && let Err(error) = fs.chmod(&temp, metadata.mode).await
+    {
+        let _ = fs.remove(&temp, false).await;
+        return Err(format!("cannot preserve file mode: {error}"));
+    }
+    #[cfg(feature = "failpoints")]
+    if injected_failure(failpoints.rename, "error") {
+        let _ = fs.remove(&temp, false).await;
+        return Err(format!(
+            "cannot replace '{}': injected failure",
+            target.display()
+        ));
+    }
+    if let Err(error) = fs.rename(&temp, target).await {
+        let _ = fs.remove(&temp, false).await;
+        return Err(format!("cannot replace '{}': {error}", target.display()));
+    }
+    #[cfg(not(feature = "failpoints"))]
+    let _ = failpoints;
+    Ok(())
+}
+
+#[cfg(feature = "failpoints")]
+fn injected_failure(name: &str, expected: &str) -> bool {
+    fail::eval(name, |action| action.as_deref() == Some(expected)).unwrap_or(false)
+}

crates/bashkit/src/builtins/limits.rs

@@ -74,6 +74,10 @@ pub(crate) const RETRY_MAX_ATTEMPTS: u32 = 10_000;
 /// sed: max group-nesting depth in `s` replacements.
 pub(crate) const SED_MAX_GROUP_NESTING_DEPTH: usize = 128;
 
+/// sed: max instructions executed for one input line, bounding `b`/`t` loops.
+/// THREAT[TM-DOS]: sed scripts are untrusted text and `:a;ba` never terminates.
+pub(crate) const SED_MAX_CYCLE_STEPS: usize = 1_000;
+
 /// sleep: max sleep duration.
 pub(crate) const SLEEP_MAX_SECONDS: f64 = 60.0;
 

crates/bashkit/src/builtins/mod.rs

@@ -26,6 +26,7 @@ mod alias;
 mod archive;
 pub(crate) mod arg_parser;
 mod assert;
+mod atomic_write;
 mod awk;
 mod base64;
 mod bc;