fix: compose bash bootstrap PROMPT_COMMAND instead of clobbering it

Replace the bootstrap's unconditional unset PROMPT_COMMAND with a
self-strip keyed on a trailing marker: remove only Programa's own
bootstrap text and keep whatever the user's startup files appended
before the first prompt (e.g. starship_precmd from
eval "$(starship init bash)"). programa-bash-integration.bash's
existing PROMPT_COMMAND merge then prepends _cmux_prompt_command,
yielding _cmux_prompt_command;starship_precmd so starship_precmd runs
on every prompt instead of being discarded after the first one.

Also add a plain-bash no-regression case alongside the fix.

Author: arzafran

Resources/shell-integration/programa-bash-bootstrap.bash

@@ -6,10 +6,24 @@
 # interactive prompt: it sources Programa's bash integration and then hands
 # control to _programa_prompt_command.
 #
+# COMPOSE, don't clobber. A user's startup files may have appended their own
+# command to PROMPT_COMMAND *after* this bootstrap before the first prompt --
+# most notably `eval "$(starship init bash)"`, which appends starship_precmd.
+# We must remove only this bootstrap and keep whatever the user appended, so
+# hooks like starship_precmd keep running on every prompt instead of being
+# wiped after the first one.
+#
+# How: strip everything up to and including the marker at the end of this
+# script (the marker is the last occurrence, so the greedy ## match lands on
+# it), which leaves exactly the user's appended tail. Then trim the leading
+# separator and let programa-bash-integration.bash's PROMPT_COMMAND merge
+# prepend _cmux_prompt_command.
+#
 # This file is the single source of truth. Sources/GhosttyTerminalView.swift
 # reads it (stripping these comments) and exports it as PROMPT_COMMAND, and
 # programaTests/GhosttyConfigTests.swift exercises it.
-unset PROMPT_COMMAND
+PROMPT_COMMAND="${PROMPT_COMMAND##*__programa_bash_bootstrap_marker__}"
+while [[ "$PROMPT_COMMAND" == [[:space:]\;]* ]]; do PROMPT_COMMAND="${PROMPT_COMMAND#?}"; done
 if [[ "${PROGRAMA_LOAD_GHOSTTY_BASH_INTEGRATION:-0}" == "1" && -n "${GHOSTTY_RESOURCES_DIR:-}" ]]; then
     _programa_ghostty_bash="$GHOSTTY_RESOURCES_DIR/shell-integration/bash/ghostty.bash"
     [[ -r "$_programa_ghostty_bash" ]] && source "$_programa_ghostty_bash"
@@ -20,3 +34,4 @@ if [[ "${PROGRAMA_SHELL_INTEGRATION:-1}" != "0" && -n "${PROGRAMA_SHELL_INTEGRAT
 fi
 unset _programa_ghostty_bash _programa_bash_integration
 if declare -F _programa_prompt_command >/dev/null 2>&1; then _programa_prompt_command; fi
+: __programa_bash_bootstrap_marker__

programaTests/GhosttyConfigTests.swift

@@ -3374,6 +3374,10 @@ final class ZshShellIntegrationHandoffTests: XCTestCase {
                 pc.contains("_cmux_prompt_command"),
                 "Programa's own prompt hook is missing from PROMPT_COMMAND at prompt \(i): <\(pc)>" + debug
             )
+            XCTAssertFalse(
+                pc.contains("__programa_bash_bootstrap_marker__"),
+                "bootstrap marker leaked into PROMPT_COMMAND at prompt \(i): <\(pc)>" + debug
+            )
         }
 
         let ps1Values = (1...3).map { fields["PS1_\($0)"] ?? "" }
@@ -3395,6 +3399,36 @@ final class ZshShellIntegrationHandoffTests: XCTestCase {
         )
     }
 
+    func testBashBootstrapInstallsPromptCommandWithoutUserHook() throws {
+        // No-regression guard: with no user PROMPT_COMMAND hook (plain bash,
+        // no Starship or similar prompt framework), the bootstrap must still
+        // install Programa's own prompt hook -- and must not leak its
+        // internal marker into PROMPT_COMMAND.
+        let fields = try runBashBootstrapDriver(withUserPromptHook: false)
+        let debug = "\n\nstdout:\n\(fields["__stdout__"] ?? "")\nstderr:\n\(fields["__stderr__"] ?? "")"
+
+        for i in 1...3 {
+            let pc = fields["PC_\(i)"] ?? ""
+            // Assert the observable contract (hook installed, bootstrap
+            // marker removed, no phantom hook) rather than the exact
+            // integration-internal string, so this stays green if
+            // programa-bash-integration.bash ever tweaks its PROMPT_COMMAND
+            // merge.
+            XCTAssertTrue(
+                pc.contains("_cmux_prompt_command"),
+                "plain-bash bootstrap did not install Programa's prompt hook at prompt \(i): <\(pc)>" + debug
+            )
+            XCTAssertFalse(
+                pc.contains("__programa_bash_bootstrap_marker__"),
+                "bootstrap marker leaked into PROMPT_COMMAND at prompt \(i): <\(pc)>" + debug
+            )
+            XCTAssertFalse(
+                pc.contains("starship_precmd"),
+                "unexpected starship hook in plain-bash PROMPT_COMMAND at prompt \(i): <\(pc)>" + debug
+            )
+        }
+    }
+
     /// Drives `Resources/shell-integration/programa-bash-bootstrap.bash`
     /// through real bash, modeling bash's "evaluate PROMPT_COMMAND before
     /// each prompt" loop directly (deterministic, no PTY needed). When