diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..916873d
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,5 @@
+# Every hook is a shebang script executed directly - a CRLF-mangled shebang
+# or an embedded \r mid-line breaks execution outright on Windows, where
+# GitHub's hosted runner defaults core.autocrlf to true on checkout (issue
+# #67). Force LF regardless of that setting or a contributor's local config.
+*.sh text eol=lf
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6119c6d..157e36d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,21 +7,44 @@ on:
 
 jobs:
   shell:
-    runs-on: ubuntu-latest
+    name: shell (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    defaults:
+      run:
+        # Claude Code executes a command hook under Git Bash on native
+        # Windows (issue #67) - this is the leg that answers "does it work
+        # there", not just "does it parse as POSIX sh".
+        shell: bash
     steps:
       - uses: actions/checkout@v4
-      - name: Install shellcheck and jq
-        run: sudo apt-get update && sudo apt-get install -y shellcheck jq
-      - name: Lint hooks and tests
+      # jq ships preinstalled on all three hosted runner images; shellcheck
+      # does not on Windows. Checked rather than assumed, same discipline as
+      # every hook's own jq-presence check.
+      - name: Ensure jq
+        run: command -v jq >/dev/null 2>&1 || { echo "jq missing on $RUNNER_OS" >&2; exit 1; }
+      # Static analysis of file content - the result doesn't depend on which
+      # OS runs it, so one leg is enough. Kept on Linux, where it's already
+      # preinstalled, rather than installing it fresh on the other two.
+      - name: Install shellcheck (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y shellcheck
+      - name: Lint hooks and tests (Linux)
+        if: runner.os == 'Linux'
         run: shellcheck -s sh hooks/*.sh tests/*.sh
-      - name: Validate JSON manifests
+      - name: Validate JSON manifests (Linux)
+        if: runner.os == 'Linux'
         run: |
           jq -e '.hooks | keys' hooks/hooks.json >/dev/null
           jq -e '.name and .version' .claude-plugin/plugin.json >/dev/null
           jq -e '.plugins' .claude-plugin/marketplace.json >/dev/null
           jq -e '.name and .version' .codex-plugin/plugin.json >/dev/null
           jq -e '.plugins' .agents/plugins/marketplace.json >/dev/null
-      - name: Check plugin version agreement
+      - name: Check plugin version agreement (Linux)
+        if: runner.os == 'Linux'
         run: |
           c=$(jq -r .version .claude-plugin/plugin.json)
           x=$(jq -r .version .codex-plugin/plugin.json)
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7f604ff..a92c7c3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,14 @@ All notable changes to throughline are documented here. Format loosely follows
 ## [Unreleased]
 
 ### Added
+- CI now runs the shell test suite on `windows-latest` and `macos-latest` in
+  addition to `ubuntu-latest` (issue #67) - previously an unmade platform
+  claim for hooks that are pure POSIX `sh`. A `.gitattributes` forces LF line
+  endings on `*.sh` regardless of the Windows runner's `core.autocrlf`
+  default, and a handful of permission-based test assertions that stage a
+  POSIX mode bit (000/444/555) are skipped on Windows/NTFS, same as the
+  existing root-bypasses-permissions skip, with the skip count reported in
+  the final summary.
 - **Stale-handoff warning** (issue #66): `SessionStart` now compares
   `HANDOFF.md`'s `Last Updated` date against the branch's latest commit and
   warns past a 14-day gap. Every handoff-file design shares this blind spot
diff --git a/hooks/session-capture.sh b/hooks/session-capture.sh
index 312798c..a0893b3 100755
--- a/hooks/session-capture.sh
+++ b/hooks/session-capture.sh
@@ -68,7 +68,27 @@ mkdir -p "$bufdir" 2>/dev/null || { tl_err "mkdir failed for buffer dir"; exit 0
 # the identical final sanitized id even in the currently-unreachable case of a
 # stranger one. A regression test locks in that capture and flush agree on the
 # filename for a tab-containing id.
-out=$(printf '%s' "$input" | jq -r --arg root "$root" "$(tl_jq_redact_defs)"'
+#
+# $root reaches jq embedded as a JSON string LITERAL inside the jq PROGRAM
+# TEXT ($root_json below), not as `--arg root "$root"` and not as an
+# environment variable either - both of those were tried and both failed
+# identically on a real Windows CI run (issue #67). On Windows Git Bash, jq
+# is a native, non-MSYS binary, and MSYS auto-converts a POSIX-looking value
+# to Windows-native form before a native executable sees it; `--arg root`
+# passes $root as its own, whole argv item - exactly what MSYS's "does this
+# whole argument look like a path" heuristic matches - and an environment
+# variable turned out to be converted the same way. The file_path being
+# compared against it arrives over stdin, which MSYS never touches, so the
+# two never matched and every path this hook wrote stayed unrelativized.
+# Embedding the value as a JSON string INSIDE the much larger jq filter
+# text - which starts with `def outcome($t): ...` and is nowhere close to
+# looking like a path as a whole argument - sidesteps the heuristic
+# entirely, whichever exact channel (argv vs. env) was actually converting
+# it. $root_json is built via a SEPARATE jq call fed over stdin (line below),
+# the one channel already confirmed immune to this, so the value it embeds
+# is the untouched original.
+root_json=$(printf '%s' "$root" | jq -Rs .)
+out=$(printf '%s' "$input" | jq -r "$(tl_jq_redact_defs)""(${root_json}) as \$proot | "'
   # Observable outcome from the tool result. The Claude Code Bash tool_response
   # exposes "interrupted" but NOT an exit code, so a plain non-zero exit is not
   # visible to a PostToolUse hook and is deliberately left unmarked rather than
@@ -94,7 +114,7 @@ out=$(printf '%s' "$input" | jq -r --arg root "$root" "$(tl_jq_redact_defs)"'
       ((.tool_input.command // "") | redact | clean | clamp(200; "…[truncated]")) + "`"
     elif ($t == "Edit" or $t == "Write" or $t == "NotebookEdit") then
       "**" + $t + "** " +
-      ((.tool_input.file_path // .tool_input.notebook_path // "?") | ltrimstr($root + "/") | redact | clean) +
+      ((.tool_input.file_path // .tool_input.notebook_path // "?") | ltrimstr($proot + "/") | redact | clean) +
       outcome($t)
     # High-signal read-side tools (issue #6): one redacted+cleaned argument
     # each, same outcome suffix. Each argument is clamped to a short prefix so
diff --git a/hooks/session-onboard.sh b/hooks/session-onboard.sh
index 738162f..a599b72 100755
--- a/hooks/session-onboard.sh
+++ b/hooks/session-onboard.sh
@@ -261,7 +261,7 @@ if [ "$in_worktree" = "1" ]; then
   git -C "$root" status -s 2>/dev/null | head -20 | awk -v max="$TL_GIT_STATUS_LINE_CHARS" '
     { if (length($0) > max) print substr($0, 1, max) " …[line truncated]"
       else print
-    }'
+    }' 2>/dev/null
   echo '```'
 fi
 
@@ -388,7 +388,7 @@ if [ "$src" = "compact" ] && [ -n "$sid" ] && [ -f "$bufdir/session-$sid.md" ];
   tail -n "$TL_COMPACT_TAIL_LINES" "$buf" 2>/dev/null | awk -v max="$TL_COMPACT_TAIL_LINE_CHARS" '
     { if (length($0) > max) print substr($0, 1, max) " …[line truncated]"
       else print
-    }'
+    }' 2>/dev/null
   echo '```'
 fi
 
diff --git a/tests/run.sh b/tests/run.sh
index 3a6936e..35f2ef6 100644
--- a/tests/run.sh
+++ b/tests/run.sh
@@ -42,6 +42,29 @@ ROOT=$(unset CDPATH; cd -- "$(dirname -- "$0")/.." && pwd)
 H="$ROOT/hooks"
 PASS=0
 FAIL=0
+SKIPPED_WINDOWS=0
+
+# A few permission-based assertions below stage a POSIX mode bit (000/444/555)
+# that NTFS's chmod emulation cannot reliably enforce the same way ext4/APFS
+# do - those are skipped on Windows, same as the existing
+# root-bypasses-permissions guard, and counted so the final summary says how
+# many were skipped rather than the count silently reading lower with no
+# explanation (the same transparency adrrr/persistent-handoff's own Windows
+# leg documents for its skips).
+#
+# review finding (issue #67): checking only MSYSTEM fails OPEN, not closed -
+# it's set by the Git-for-Windows wrapper bash.exe hands off to, not by the
+# MSYS runtime itself, so anything invoking usr/bin/sh.exe or usr/bin/bash.exe
+# directly (a plausible shape for how a harness spawns a command hook, and
+# exactly the scenario this issue exists to cover) leaves it unset and the
+# guards below would silently stop firing. `uname -s` (MINGW*/MSYS*/CYGWIN*)
+# and $OS=Windows_NT come from the kernel/process environment directly, not a
+# wrapper script, so either backstops the case MSYSTEM alone misses.
+is_windows() {
+  case "$(uname -s 2>/dev/null)" in MINGW*|MSYS*|CYGWIN*) return 0 ;; esac
+  [ -n "${MSYSTEM:-}" ] || [ "${OS:-}" = "Windows_NT" ]
+}
+skip_win() { SKIPPED_WINDOWS=$((SKIPPED_WINDOWS + 1)); ok "$1 (skipped: NTFS chmod can't stage this)"; }
 
 WORK=$(mktemp -d 2>/dev/null || echo "/tmp/tl-tests.$$")
 mkdir -p "$WORK/proj/.claude/throughline/buffer"
@@ -282,9 +305,19 @@ E=$(grep Edit "$BUF/session-T.md")
 has   "Edit path is relativized to project root" "$E" 'src/app.js'
 hasnt "Edit path drops the absolute prefix" "$E" "$WORK"
 cap '{"session_id":"T","tool_name":"Write","tool_input":{"file_path":"'"$WORK"'/proj/src/new.js"}}'
-has "Write path is relativized to project root" "$(grep '\*\*Write\*\*' "$BUF/session-T.md")" 'src/new.js'
+W=$(grep '\*\*Write\*\*' "$BUF/session-T.md")
+has   "Write path is relativized to project root" "$W" 'src/new.js'
+# review finding: only the Edit assertion above checked for the ABSENCE of
+# the absolute prefix - Write and NotebookEdit share the identical
+# relativization code path and would fail identically (as they briefly did
+# on Windows, per env.root vs. --arg root above) without anyone catching it,
+# since "the tail is present" alone stays true even when the prefix was
+# never stripped.
+hasnt "Write path drops the absolute prefix" "$W" "$WORK"
 cap '{"session_id":"T","tool_name":"NotebookEdit","tool_input":{"notebook_path":"'"$WORK"'/proj/nb/a.ipynb"}}'
-has "NotebookEdit uses notebook_path fallback" "$(grep NotebookEdit "$BUF/session-T.md")" 'nb/a.ipynb'
+NB=$(grep NotebookEdit "$BUF/session-T.md")
+has   "NotebookEdit uses notebook_path fallback" "$NB" 'nb/a.ipynb'
+hasnt "NotebookEdit path drops the absolute prefix" "$NB" "$WORK"
 cap '{"session_id":"T","tool_name":"Write","tool_input":{}}'
 has "Write with neither path key falls back to ?" "$(grep '\*\*Write\*\* ?' "$BUF/session-T.md")" '**Write** ?'
 
@@ -486,12 +519,19 @@ before "onboard(compact) live git state precedes the buffer-tail inline" \
 #      path is truncated per-line the same way an oversized buffer-tail line
 #      already is (7c below), keeping this block bounded on both axes the
 #      way its "renders first, has no fallback" placement (7b2) assumes.
+# Path length is tuned deliberately, not just "as long as possible": the
+# repo-relative path needs to push a git-status line past
+# TL_GIT_STATUS_LINE_CHARS=200, but the FULL filesystem path (this fixture's
+# $WORK prefix included) must stay under Windows' classic 260-character
+# MAX_PATH - review finding: the original version of this fixture exceeded
+# it and failed to even stage on Windows CI (git init/add/commit itself
+# failed), never reaching the assertion this test exists to make.
 FRESH_LONGPATH="$WORK/fresh-longpath"
-LONGPATH="a/very/deeply/nested/directory/structure/that/goes/on/for/quite/a/while/to/simulate/a/real/monorepo/with/excessively/long/generated/paths"
-LONGNAME="a_very_long_generated_filename_that_pushes_this_line_well_past_two_hundred_characters_in_length.txt"
+LONGPATH="a/very/deeply/nested/directory/structure/for/testing"
+LONGNAME="a_generated_file_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.txt"
 mkdir -p "$FRESH_LONGPATH/$LONGPATH"
 : > "$FRESH_LONGPATH/$LONGPATH/$LONGNAME"
-( cd "$FRESH_LONGPATH" && git init -q && git add -A && git commit -q -m init ) 2>/dev/null \
+( cd "$FRESH_LONGPATH" && git init -q && git config core.longpaths true && git add -A && git commit -q -m init ) 2>/dev/null \
   || bad "fixture setup failed: $FRESH_LONGPATH (git init/add/commit)"
 printf -- 'changed\n' >> "$FRESH_LONGPATH/$LONGPATH/$LONGNAME"
 O_LONGPATH=$(printf '%s' '{"source":"startup","session_id":"T"}' | CLAUDE_PROJECT_DIR="$FRESH_LONGPATH" sh "$H/session-onboard.sh")
@@ -571,8 +611,12 @@ has "a buffer with zero conforming lines is still counted, not dropped" "$O3a4"
 # rather than feeding an empty operand to the integer test, which would
 # otherwise leak a shell diagnostic to stderr, breaking this hook's
 # always-silent-on-error contract (every other error path here is
-# 2>/dev/null'd). Skipped when running as root, which bypasses permissions.
-if [ "$(id -u)" != "0" ]; then
+# 2>/dev/null'd). Skipped when running as root, which bypasses permissions,
+# or on Windows/NTFS, which can't stage an unreadable-to-owner file (see
+# is_windows() above).
+if is_windows; then
+  skip_win "unreadable-buffer stderr test"
+elif [ "$(id -u)" != "0" ]; then
   reset_buf
   printf -- '- x\n' > "$BUF/session-T.md"
   printf 'test' > "$BUF/session-UNREAD.md"
@@ -606,9 +650,18 @@ has   "no-end-stamp buffer surfaced with hedged wording" "$O3b" 'no end-stamp'
 hasnt "no-end-stamp buffer NOT mislabeled as ended" "$O3b" 'ended without'
 
 # 11. missing jq surfaces a visible warning in onboard (curated PATH without jq)
+# A tiny exec wrapper script per tool, not `ln -sf` or `cp`: a symlink needs
+# an elevated privilege Windows doesn't grant by default (issue #67), and a
+# COPY of the real binary is worse - on macOS a Homebrew-built binary can
+# resolve its shared libraries via an @executable_path-relative reference,
+# which breaks (hangs or crashes) once the binary is relocated to $STUB. A
+# plain `#!/bin/sh -c 'exec <real> "$@"'` wrapper needs no privilege beyond
+# writing a text file and never touches the real binary's own location.
 STUB="$WORK/bin"; mkdir -p "$STUB"
-for c in sh dirname cat grep git tr head; do
-  real=$(command -v "$c" 2>/dev/null) && ln -sf "$real" "$STUB/$c"
+for c in sh dirname cat grep git tr head awk; do
+  real=$(command -v "$c" 2>/dev/null) || continue
+  printf '#!/bin/sh\nexec "%s" "$@"\n' "$real" > "$STUB/$c"
+  chmod +x "$STUB/$c"
 done
 O4=$(printf '%s' '{"source":"startup","session_id":"T"}' | PATH="$STUB" sh "$H/session-onboard.sh")
 has "onboard warns when jq is missing" "$O4" 'jq'
@@ -678,7 +731,11 @@ present "capture-first auto-activates and writes a buffer entry" "$FRESH_D/.clau
 FRESH_E="$WORK/fresh-e"
 mkdir -p "$FRESH_E"
 fixture_repo "$FRESH_E"
-if [ "$(id -u)" != "0" ]; then
+if is_windows; then
+  skip_win "failed-bootstrap warning test"
+  skip_win "failed-bootstrap no-dir-created test"
+  skip_win "failed-bootstrap path-relativization test"
+elif [ "$(id -u)" != "0" ]; then
   chmod 555 "$FRESH_E" 2>/dev/null
   O8=$(printf '%s' '{"source":"startup","session_id":"T"}' | CLAUDE_PROJECT_DIR="$FRESH_E" sh "$H/session-onboard.sh")
   chmod 755 "$FRESH_E" 2>/dev/null
@@ -1066,5 +1123,6 @@ eq "precompact: boundary after a post-boundary action stamps again" "$(grep -c '
 
 echo "----------------------"
 printf 'passed: %s   failed: %s\n' "$PASS" "$FAIL"
+[ "$SKIPPED_WINDOWS" -eq 0 ] || printf '  (%s permission-based assertion(s) skipped on Windows/NTFS - see is_windows() above)\n' "$SKIPPED_WINDOWS"
 rm -rf "$WORK"
 [ "$FAIL" -eq 0 ]