diff --git a/plugins/source-control/.claude-plugin/plugin.json b/plugins/source-control/.claude-plugin/plugin.json
index 8c485fc94..4cc220f23 100644
--- a/plugins/source-control/.claude-plugin/plugin.json
+++ b/plugins/source-control/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/claude-code-plugin-manifest.json",
   "name": "source-control",
-  "version": "0.26.5",
+  "version": "0.26.6",
   "description": "Git and GitHub delivery workflow: /commit (Conventional Commits + Co-Authored-By trailer via safe heredoc mechanics), /pull-request (prep, create, CI monitoring, review-comment triage, merge, CI-log fetch), /babysit-prs (self-pacing fleet loop — safe by default; opt-in worker/autopilot tiers add gate-checked merge and thread resolution behind a deterministic Python engine), /babysit-loop (the loop-lane merge lane: a standing or drain loop that invokes babysit-prs per cycle, configured through repo-scoped babysit_loop_* keys on the layered source-control.md seam, with merge authority human-only until the target repo's tracked config adopts the lane, a gate-proven C2-mechanical baseline once adopted, and merge-rung raises binding from the team-tracked layer only), /worktree (create, status, cleanup, audit for parallel-session isolation), /setup (check the effective commit-subject / PR-title convention merged across its config layers and the babysit-prs config, or apply — interview the repo and write the convention config to a chosen layer), and /resolve-conflicts (intent-first merge/rebase conflict resolution with a semantic-conflict sweep — never --abort). The commit-subject / PR-title convention is configurable via a source-control.md config written by a re-runnable setup skill, layered across a ~/.claude user-global file, the tracked team file, and a gitignored .claude/source-control.local.md personal overlay merged per key; Conventional Commits is the default when no convention is declared.",
   "author": {
     "name": "Melodic Software",
diff --git a/plugins/source-control/CHANGELOG.md b/plugins/source-control/CHANGELOG.md
index 688d32cba..c6917012c 100644
--- a/plugins/source-control/CHANGELOG.md
+++ b/plugins/source-control/CHANGELOG.md
@@ -3,6 +3,33 @@
 All notable changes to the `source-control` plugin are documented here. Format follows
 [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); this plugin uses semantic versioning.
 
+## [0.26.6]
+
+### Fixed
+
+- **`scripts/worktree-create.sh` now refuses a git-illegal `--name` with the documented usage exit 2
+  instead of environment exit 4 (`#1016`).** The up-front character class (letters, digits, dots,
+  underscores, dashes per `/`-separated segment) is not a subset of git's ref grammar, so names like
+  `feat/foo..bar`, `foo.lock`, `.foo`, `HEAD`, and `-lead` passed validation, reached
+  `git worktree add`, and failed there as exit 4 — the code the helper reserves for environment
+  faults. A caller's correction flow keys on exit 2, so an invalid name was indistinguishable from a
+  broken environment. The schema check is now followed by `git check-ref-format --branch`, whose
+  output is discarded on both streams: on success `--branch` echoes the name to stdout, which would
+  break the helper's "created path is the sole stdout line" output contract. Verified across every
+  name the character class admits, `check-ref-format` and `git worktree add -b` agree exactly, so no
+  previously-creatable name is newly refused. `skills/worktree/context/create.md` gains the matching
+  constraint bullet, and the header comment that claimed the character class was "a strict subset of
+  what git refs allow" is corrected.
+
+  The grammar check runs **after** the repository is resolved and is scoped with `-C "$toplevel"`:
+  `--branch` takes a branchname-shorthand and so performs repository discovery, which dies outright
+  when the process's CWD is a stale checkout (a `.git` file naming a gitdir that no longer exists —
+  what this plugin's own worktree cleanup handles). Run unscoped, that turned a valid name into a
+  false exit 2 from such a directory, and the documented invocation omits `--repo-dir`, so the CWD is
+  the default. Consequence: exits 3 (root unconfigured) and 4 (not a repository) can now precede the
+  grammar refusal, matching how the pre-existing `--base-ref` and empty-slug exit-2 checks already
+  sit after them. The character-class and length checks still run first, before any git call.
+
 ## [0.26.5]
 
 ### Fixed
diff --git a/plugins/source-control/scripts/worktree-create.sh b/plugins/source-control/scripts/worktree-create.sh
index a2d80971c..36dc9a152 100755
--- a/plugins/source-control/scripts/worktree-create.sh
+++ b/plugins/source-control/scripts/worktree-create.sh
@@ -26,7 +26,7 @@
 #
 # Exit codes:
 #   0  success — worktree created; path on stdout
-#   2  usage error — unknown/missing flag
+#   2  usage error — unknown/missing flag, or a --name git rejects as a branch
 #   3  refuse — external root unconfigured (guidance on stderr); nothing created
 #   4  environment error — not a git repo, or `git worktree add` failed
 
@@ -43,6 +43,13 @@ Usage:
 
 Options:
   --name <name>       Branch/worktree name (e.g. feat/my-feature). Required.
+                      Max 64 chars; each /-separated segment holds only letters,
+                      digits, dots, underscores, and dashes. Also checked against
+                      git's own branch-name grammar, so a name that satisfies the
+                      character rules but is an illegal ref (feat/foo..bar,
+                      foo.lock, HEAD) is refused (exit 2), not left to git later.
+                      That grammar check runs after the repository is resolved,
+                      so exits 3 and 4 can precede it.
   --root <dir>        External worktree root. Required and must be configured;
                       an empty value or an unexpanded \${user_config.*} token
                       makes the helper refuse (exit 3) rather than fall back to
@@ -95,10 +102,9 @@ fi
 
 # Validate the name up front against the EnterWorktree schema: max 64 chars, and
 # each '/'-separated segment contains only letters, digits, dots, underscores,
-# and dashes. This is a strict subset of what git refs allow, so a validated name
-# is always a creatable branch — reject invalid names loudly (exit 2) here rather
-# than let `git worktree add` fail opaquely downstream. The branch is used
-# verbatim; only the directory slug transforms it.
+# and dashes. Reject invalid names loudly (exit 2) here rather than let
+# `git worktree add` fail opaquely downstream. The branch is used verbatim; only
+# the directory slug transforms it.
 if (( ${#name} > 64 )); then
   printf '%s: --name %q exceeds 64 characters\n' "$PROG" "$name" >&2
   exit 2
@@ -108,6 +114,9 @@ if [[ ! "$name" =~ ^[A-Za-z0-9._-]+(/[A-Za-z0-9._-]+)*$ ]]; then
   exit 2
 fi
 
+# The remaining name check — git's own ref grammar — needs a healthy repository
+# to run in, so it waits until $toplevel is resolved below.
+
 # Refuse-with-guidance: unconfigured root. Treat an empty value or an unexpanded
 # ${user_config.*} token (what Claude Code leaves when the key is unset) as unset.
 # SC2016: the single-quoted ${user_config token is matched literally on purpose —
@@ -152,6 +161,31 @@ if ! toplevel=$(git -C "$repo_dir" rev-parse --show-toplevel 2>/dev/null); then
   exit 4
 fi
 
+# Second half of name validation: the character class checked above is NOT a
+# subset of git's ref grammar, so it alone cannot uphold the exit-2-for-an-
+# invalid-name contract. `feat/foo..bar` (`..`), `.foo` and `feat/.` (component
+# starting/ending with `.`), `foo.lock` (reserved suffix), `HEAD`, and `-lead`
+# all sit inside the class yet are illegal refs, and would otherwise fail inside
+# `git worktree add` as environment exit 4 — which a caller cannot tell from a
+# genuinely broken environment. Ask git rather than reimplementing its rules.
+#
+# Runs HERE, not beside the character check, and scoped with `-C "$toplevel"`:
+# `--branch` takes a branchname-shorthand and so performs repository discovery,
+# which fails outright when the process's CWD is a stale checkout (a `.git` file
+# naming a gitdir that no longer exists — precisely what this plugin's own
+# worktree cleanup deals with). Inheriting that CWD turned a perfectly valid name
+# into a false exit 2, and the documented invocation omits `--repo-dir`, so the
+# CWD is the default. Deferring past the exit-4 repository probe guarantees a
+# healthy repo to run in and makes a non-zero exit mean the NAME, nothing else.
+# Both streams are discarded: on success `--branch` echoes the name to stdout,
+# which would corrupt the sole-stdout-line output contract, and on failure git's
+# message is superseded by ours. An option-shaped name is read as a ref because
+# git parses no further options after `--branch`.
+if ! git -C "$toplevel" check-ref-format --branch "$name" >/dev/null 2>&1; then
+  printf '%s: --name %q is not a valid git branch name (see: git help check-ref-format)\n' "$PROG" "$name" >&2
+  exit 2
+fi
+
 # parse_owner_repo <url> — derive an `owner<TAB>repo` pair from a remote URL for
 # the directory name. Sets globals `owner` and `repo`. Handles the shapes we see:
 #   git@host:owner/repo.git · https://host/owner/repo.git · ssh://git@host/owner/repo
diff --git a/plugins/source-control/scripts/worktree-create.test.sh b/plugins/source-control/scripts/worktree-create.test.sh
index 799341881..3ba6014c9 100755
--- a/plugins/source-control/scripts/worktree-create.test.sh
+++ b/plugins/source-control/scripts/worktree-create.test.sh
@@ -273,6 +273,36 @@ assert_contains "unsafe-char refusal explains the rule" "$err" "not a valid work
 # An over-long name (>64 chars) is likewise refused.
 bash "$HELPER" --name "feat/$(printf 'a%.0s' {1..70})" --root "$TEST_TMPDIR/wtroot10" --repo-dir "$repo" >/dev/null 2>&1
 assert_exit "over-64-char name refused (exit 2)" 2 "$?"
+# A name whose characters are all in the allowed class but which git rejects as a
+# branch is refused here (exit 2) rather than reaching `git worktree add` and
+# surfacing as environment exit 4 — the correction flow keys on the usage error.
+for badref in 'feat/foo..bar' 'feat/.' 'foo.lock' 'feat/x.lock' '.foo' 'foo.' 'HEAD' '-lead'; do
+  code=0
+  err=$(bash "$HELPER" --name "$badref" --root "$TEST_TMPDIR/wtroot10c" --repo-dir "$repo" 2>&1 >/dev/null) || code=$?
+  assert_exit "git-invalid ref name $badref refused (exit 2, not 4)" 2 "$code"
+  assert_contains "git-invalid $badref refusal names the branch grammar" "$err" "not a valid git branch name"
+done
+# The ref check must not eat stdout: `git check-ref-format --branch` echoes the
+# name on success, which would corrupt the sole-stdout-line path contract.
+root="$TEST_TMPDIR/wtroot10d"
+out=$(bash "$HELPER" --name "feat/refok" --root "$root" --repo-dir "$repo" 2>/dev/null)
+assert_exit "ref-valid name still creates (exit 0)" 0 "$?"
+assert_eq "ref check leaves stdout as the sole path line" "$root/acme-widget-feat-refok" "$out"
+# `check-ref-format --branch` takes a branchname-shorthand, so it does repository
+# discovery and dies when the process CWD is a stale checkout (a .git file naming
+# a gitdir that no longer exists). Scoping it to $toplevel keeps a VALID name from
+# being rejected because of where the caller happened to stand — the documented
+# invocation omits --repo-dir, so the CWD is the default.
+stale="$(mktemp -d "$TEST_TMPDIR/staleXXXXXX")"
+printf 'gitdir: %s/definitely-not-here\n' "$TEST_TMPDIR" > "$stale/.git"
+root="$TEST_TMPDIR/wtroot10e"
+out=$(cd "$stale" && bash "$HELPER" --name "feat/cwdok" --root "$root" --repo-dir "$repo" 2>/dev/null)
+assert_exit "valid name unaffected by a stale .git in the CWD (exit 0)" 0 "$?"
+assert_eq "stale-CWD run still prints the worktree path" "$root/acme-widget-feat-cwdok" "$out"
+# ...and an invalid name is still caught from that same stale CWD.
+code=0
+(cd "$stale" && bash "$HELPER" --name 'feat/foo..bar' --root "$TEST_TMPDIR/wtroot10f" --repo-dir "$repo") >/dev/null 2>&1 || code=$?
+assert_exit "stale CWD still rejects a git-invalid name (exit 2)" 2 "$code"
 # A valid multi-segment name keeps the branch verbatim but transforms the slug.
 root="$TEST_TMPDIR/wtroot10b"
 out=$(bash "$HELPER" --name "feat/scope.v2_final-1" --root "$root" --repo-dir "$repo" 2>/dev/null)
diff --git a/plugins/source-control/skills/worktree/context/create.md b/plugins/source-control/skills/worktree/context/create.md
index 0c5865ff6..b79f76a14 100644
--- a/plugins/source-control/skills/worktree/context/create.md
+++ b/plugins/source-control/skills/worktree/context/create.md
@@ -21,6 +21,7 @@ The name (branch and, via the helper's slug, directory) has these constraints (t
 - Each `/`-separated segment may contain only **letters, digits, dots, underscores, and dashes**
 - Max **64 characters** total
 - `/` is a valid segment separator (enables `feat/my-feature` format)
+- The name must also be a **legal git branch name** (`git check-ref-format --branch`). The character rule above does not imply this — `feat/foo..bar`, `foo.lock`, `.foo`, `HEAD`, and `-lead` all satisfy it yet git rejects them as refs. The helper checks this after resolving the repository, so exits 3 and 4 can precede an invalid-name exit 2.
 
 Validate the name against these rules. If invalid, explain what's wrong and ask for correction. The helper re-validates defensively and **refuses** a name that violates them (exit 2) rather than let `git worktree add` fail opaquely. The branch keeps the name verbatim; the helper derives the **directory slug** from it (each `/` → `-`).