## Why
`build_prompt_input` now initializes `ExecServerRuntimePaths`, which
requires a configured Codex executable path. The previous inline unit
test in `core/src/prompt_debug.rs` built a bare `test_config()` and then
failed before it could assert anything useful:
```text
Codex executable path is not configured
```
This coverage is also integration-shaped: it drives the public
`build_prompt_input` entry point through config, thread, and session
setup rather than testing a small internal helper in isolation.
Bazel CI did not catch this earlier because the affected test was behind
the same wrapped Rust unit-test path fixed by #18913. Before that
launcher/sharding fix, the outer `workspace_root_test` changed the
working directory for Insta compatibility while the inner `rules_rust`
sharding wrapper still expected its runfiles working directory. In
practice, Bazel could report success without executing the Rust test
cases in that shard. Once #18913 makes the wrapper run the Rust test
binary directly and shard with libtest arguments, this stale unit test
actually runs and exposes the missing `codex_self_exe` setup.
## What Changed
- Moved `build_prompt_input_includes_context_and_user_message` out of
`core/src/prompt_debug.rs`.
- Added `core/tests/suite/prompt_debug_tests.rs` and registered it from
`core/tests/suite/mod.rs`.
- Builds the test config with `ConfigBuilder` and provides
`codex_self_exe` using the current test executable, matching the
runtime-path invariant required by prompt debug setup.
- Preserves the existing assertions that the generated prompt input
includes both the debug user message and project-specific user
instructions.
## Verification
- `cargo test -p codex-core --test all
prompt_debug_tests::build_prompt_input_includes_context_and_user_message`
- `bazel test //codex-rs/core:core-all-test
--test_arg=prompt_debug_tests::build_prompt_input_includes_context_and_user_message
--test_output=errors`
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/18916).
* #18913
* __->__ #18916
Extract a shared helper that builds AuthManager from Config and applies
the forced ChatGPT workspace override in one place.
Create the shared AuthManager at MessageProcessor call sites so that
upcoming new transport's initialization can reuse the same handle, and
keep only external auth refresher wiring inside `MessageProcessor`.
Remove the now-unused `AuthManager::shared_with_external_auth` helper.
This PR adds root and profile config switches to omit the generated
`<permissions instructions>` and `<apps_instructions>` prompt blocks
while keeping both enabled by default, and it gates both the initial
developer-context injection and later permissions diff injection so
turning the permissions block off stays effective across turn-context
overrides.
Also added a prompt debug tool that can be used as `codex debug
prompt-input "hello"` and dumps the constructed items list.
