diff --git a/IMPLEMENTATION_PLAN.md b/IMPLEMENTATION_PLAN.md
index f426100..2354ffc 100644
--- a/IMPLEMENTATION_PLAN.md
+++ b/IMPLEMENTATION_PLAN.md
@@ -565,9 +565,10 @@ priorities.
       mutating or ambiguous `hash`, `alias`, `unalias`, `shopt`, and `enable`
       forms before later occurrences can inherit a false executable identity; retain only
       exact static query grammar and pin native-shell behavior, recursive
-      wrappers, and executable corpus cases. Fail unmodeled `time`, negation,
-      coprocess, and current-shell brace-group syntax closed rather than
-      flattening nested execution into apparent ordinary verb chains.
+      wrappers, and executable corpus cases. Entries 273-280 pin the mutation
+      and reserved-form boundaries, including unmodeled `time`, negation,
+      coprocess, and current-shell brace-group syntax, which fail closed rather
+      than flattening nested execution into apparent ordinary verb chains.
 - [ ] Promote the Bash command-resolution mutation cases into Netclaw's strict
       allow/prompt/deny matrix before the downstream approval-fatigue gate.
 - [x] Add the separately tested Bash `<<<` here-string redirect slice with
diff --git a/tests/ShellSyntaxTree.Tests/Corpus/bash/280_v03_coproc_rejected.json b/tests/ShellSyntaxTree.Tests/Corpus/bash/280_v03_coproc_rejected.json
new file mode 100644
index 0000000..ff7b9eb
--- /dev/null
+++ b/tests/ShellSyntaxTree.Tests/Corpus/bash/280_v03_coproc_rejected.json
@@ -0,0 +1,10 @@
+{
+  "name": "v0.3 Bash coprocess form fails closed before nested command",
+  "input": "coproc git status",
+  "expected": {
+    "isUnparseable": true,
+    "unparseableReasonContains": "reserved execution syntax"
+  },
+  "notes": "A coprocess starts asynchronous execution with pipe state that stable v0.3 does not model, so its command body cannot be treated as an ordinary complete command.",
+  "oracleExpectation": "OutOfScope"
+}