fix(install): only manage strix in the installer's own directory

`check_existing_installation` walked `which -a strix` and deleted every
match outside `$INSTALL_DIR`, and `verify_installation` deleted whatever
executable won PATH resolution. Path discovery shows that another `strix`
exists; it does not show that the installer owns it. A pipx install or a
development checkout on `PATH` was removed without being asked about,
including a `pipx uninstall strix-agent` triggered purely by the path
containing `.local/bin`.

The installer now touches only `$INSTALL_DIR`. Other executables are
reported, and when one wins PATH resolution the user is told how to
reorder `PATH` or remove it themselves.

Fixes #1262

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/install.sh

@@ -99,33 +99,35 @@ print_message() {
     echo -e "${color}${message}${NC}"
 }
 
+describe_removal() {
+    local path=$1
+
+    if [[ "$path" == *".local/bin"* ]] && command -v pipx >/dev/null 2>&1; then
+        echo -e "${MUTED}  It looks like a pipx installation. To remove it: ${NC}pipx uninstall strix-agent"
+    else
+        echo -e "${MUTED}  To remove it: ${NC}rm $path"
+    fi
+}
+
 check_existing_installation() {
+    UNMANAGED_INSTALLATIONS=()
+
     local found_paths=()
     while IFS= read -r -d '' path; do
         found_paths+=("$path")
     done < <(which -a strix 2>/dev/null | tr '\n' '\0' || true)
 
-    if [ ${#found_paths[@]} -gt 0 ]; then
-        for path in "${found_paths[@]}"; do
-            if [[ ! -e "$path" ]] || [[ "$path" == "$INSTALL_DIR/strix"* ]]; then
-                continue
-            fi
+    for path in "${found_paths[@]:-}"; do
+        if [[ -z "$path" ]] || [[ ! -e "$path" ]] || [[ "$path" == "$INSTALL_DIR/strix"* ]]; then
+            continue
+        fi
 
-            if [[ -n "$path" ]]; then
-                echo -e "${MUTED}Found existing strix at: ${NC}$path"
+        UNMANAGED_INSTALLATIONS+=("$path")
+        echo -e "${MUTED}Found another strix at: ${NC}$path"
+    done
 
-                if [[ "$path" == *".local/bin"* ]]; then
-                    echo -e "${MUTED}Removing old pipx installation...${NC}"
-                    if command -v pipx >/dev/null 2>&1; then
-                        pipx uninstall strix-agent 2>/dev/null || true
-                    fi
-                    rm -f "$path" 2>/dev/null || true
-                elif [[ -L "$path" || -f "$path" ]]; then
-                    echo -e "${MUTED}Removing old installation...${NC}"
-                    rm -f "$path" 2>/dev/null || true
-                fi
-            fi
-        done
+    if [ ${#UNMANAGED_INSTALLATIONS[@]} -gt 0 ]; then
+        echo -e "${MUTED}This installer only manages ${NC}$INSTALL_DIR${MUTED}, so it is left alone.${NC}"
     fi
 }
 
@@ -296,15 +298,10 @@ verify_installation() {
 
     if [[ "$which_strix" != "$INSTALL_DIR/strix" && "$which_strix" != "$INSTALL_DIR/strix.exe" ]]; then
         if [[ -n "$which_strix" ]]; then
-            echo -e "${YELLOW}⚠ Found conflicting strix at: ${NC}$which_strix"
-            echo -e "${MUTED}Attempting to remove...${NC}"
-
-            if rm -f "$which_strix" 2>/dev/null; then
-                echo -e "${GREEN}✓ Removed conflicting installation${NC}"
-            else
-                echo -e "${YELLOW}Could not remove automatically.${NC}"
-                echo -e "${MUTED}Please remove manually: ${NC}rm $which_strix"
-            fi
+            echo -e "${YELLOW}⚠ Another strix wins PATH resolution: ${NC}$which_strix"
+            echo -e "${MUTED}The version just installed lives in ${NC}$INSTALL_DIR${MUTED} and will not run until that changes.${NC}"
+            echo -e "${MUTED}Put ${NC}$INSTALL_DIR${MUTED} earlier on your PATH, or remove the other executable yourself.${NC}"
+            describe_removal "$which_strix"
         fi
     fi
 

tests/test_install_script.py

@@ -152,3 +152,46 @@ def test_installer_rejects_unsupported_architecture(tmp_path: Path) -> None:
     assert "Unsupported OS/Arch: linux/riscv64" in result.stdout
     assert not curl_log_path.exists()
     assert not (home_path / ".strix").exists()
+
+
+def _install_with_decoy(tmp_path: Path, decoy_directory_name: str) -> tuple[Path, Path, Path]:
+    """Run the installer with an unrelated `strix` ahead of it on `PATH`."""
+    repository_root = Path(__file__).resolve().parents[1]
+    archive_path = _create_release_archive(tmp_path)
+    mock_bin = _create_mock_commands(tmp_path, machine="aarch64")
+
+    pipx_log_path = tmp_path / "pipx.log"
+    _write_executable(
+        mock_bin / "pipx",
+        f'#!/bin/sh\nprintf \'%s\n\' "$*" >> "{pipx_log_path}"\n',
+    )
+
+    decoy_directory = tmp_path / decoy_directory_name
+    decoy_directory.mkdir(parents=True)
+    decoy_path = decoy_directory / "strix"
+    _write_executable(decoy_path, "#!/bin/sh\nprintf 'other-strix 1.2.3\n'\n")
+
+    environment, home_path, _ = _create_installer_environment(tmp_path, archive_path, mock_bin)
+    environment["PATH"] = f"{decoy_directory}:{environment['PATH']}"
+
+    result = _run_installer(repository_root, environment)
+    assert result.returncode == 0, result.stderr
+
+    return decoy_path, pipx_log_path, home_path
+
+
+def test_installer_leaves_unrelated_strix_executables_alone(tmp_path: Path) -> None:
+    decoy_path, pipx_log_path, home_path = _install_with_decoy(tmp_path, "other-bin")
+
+    assert decoy_path.exists()
+    assert decoy_path.read_text(encoding="utf-8") == "#!/bin/sh\nprintf 'other-strix 1.2.3\n'\n"
+    assert not pipx_log_path.exists()
+    assert (home_path / ".strix/bin/strix").exists()
+
+
+def test_installer_does_not_uninstall_a_pipx_managed_strix(tmp_path: Path) -> None:
+    decoy_path, pipx_log_path, home_path = _install_with_decoy(tmp_path, ".local/bin")
+
+    assert decoy_path.exists()
+    assert not pipx_log_path.exists()
+    assert (home_path / ".strix/bin/strix").exists()