feat(rewrite): rewrite in pipe when consummer is safe

docs/contributing/TECHNICAL.md

@@ -143,8 +143,10 @@ rewrite_compound(cmd, excluded)                    [src/discover/registry.rs]
   |
   |  Step 2 — Split on operators, rewrite each segment
   |  Operator (&&, ||, ;) → rewrite both sides
-  |  Pipe (|) → keep producers/intermediate stages raw
-  |             rewrite only a pipeline-safe final stage
+  |  Pipe (|) → keep intermediate stages raw
+  |             rewrite a pipeline-safe final stage, or the
+  |             producer when its rule allows it and all
+  |             consumers are display-only (#3171)
   |  Stderr pipe (|&) → keep the complete pipeline raw
   |  Shellism (&) → rewrite both sides (background)
   |

src/discover/README.md

@@ -21,7 +21,7 @@ When a hook sends `cargo fmt --all && cargo test 2>&1 | tail -20`:
 → [Arg("cargo"), Arg("test"), Redirect("2>&1"), Operator("&&"), Arg("git"), Arg("status")]
 ```
 
-**Compound splitting** — The rewrite engine walks the tokens, splitting on `Operator` (`&&`, `||`, `;`) and typed `Pipe` tokens (`|`, `|&`). For normal pipelines, producers and intermediate stages stay raw, and only an argument-safe final stage marked `pipeline_final_safe` is rewritten. The initial safe set is ordinary `grep` and `rg` invocations; search pattern-file forms (`-f`/`--file`) defer because they can consume pipeline stdin as configuration. Stderr pipelines (`|&`) and pipelines containing opaque shell groups remain raw.
+**Compound splitting** — The rewrite engine walks the tokens, splitting on `Operator` (`&&`, `||`, `;`) and typed `Pipe` tokens (`|`, `|&`). For normal pipelines, intermediate stages stay raw. A final stage whose rule's `pipeline_safety` allows it (ordinary `grep` and `rg` invocations) is rewritten; search pattern-file forms (`-f`/`--file`) defer because they can consume pipeline stdin as configuration. The producer stage is rewritten when its rule's `pipeline_safety` allows it and every downstream stage is a display-only consumer (`cat`, `head`, non-following `tail`) with no file-target redirect (#3171). Stderr pipelines (`|&`) and pipelines containing opaque shell groups remain raw.
 
 **Per-segment rewriting** — Each segment goes through:
 

src/discover/lexer.rs

@@ -332,7 +332,7 @@ fn contains_substitution(cmd: &str) -> bool {
 
 // `>&N`/`>&-` (and `N>&M`) is fd-dup/close; bare `>&` before a word is
 // `>word 2>&1` — a file target.
-fn redirect_has_file_target(tokens: &[ParsedToken], i: usize) -> bool {
+pub(crate) fn redirect_has_file_target(tokens: &[ParsedToken], i: usize) -> bool {
     let value = &tokens[i].value;
     if let Some(pos) = value.find(">&") {
         let tail = &value[pos + 2..];