fix: repair managed Git launchers in sandbox projects (#13588)

## Thinking Path

> - Paperclip runs agents in local and remote execution environments.
> - Managed GitHub launchers select credentials for each Git operation.
> - Remote launchers are written inside the project checkout as
extensionless CommonJS scripts.
> - An ES module project makes Node interpret those launchers as ESM, so
they crash before credential resolution.
> - When the launcher can start, empty identity variables also override
valid repository and command-line Git configuration.
> - This change gives the launchers their own CommonJS scope and clears
empty identity overrides while preserving managed credential isolation.

## Linked Issues or Issue Description

**What happened?**

In a repository with `"type": "module"`, the managed `git` and `gh`
launchers fail immediately with `ReferenceError: require is not defined
in ES module scope`. The launchers use CommonJS but inherited the
enclosing project's module type.

Sandbox agents also report empty `GIT_AUTHOR_NAME` and
`GIT_COMMITTER_NAME` variables and try to unset them for each command.
With no managed identity available, the Git launcher recreated those
empty values. `git commit` failed with `fatal: empty ident name`, even
with explicit `user.name` and `user.email` configuration.

**Expected behavior**

Managed `git` and `gh` start in both ES module and CommonJS projects.
Local commits with an explicitly configured identity work without manual
environment cleanup. Managed credentials and captured identity continue
to take precedence. Missing identity does not silently select the host
user's details.

**Steps to reproduce**

1. Create a sandbox project whose `package.json` contains `"type":
"module"`.
2. Stage the managed GitHub launchers and run `git --version` or `gh
--version`. Before this fix, the launcher fails at its first
`require()`.
3. In a CommonJS project with no available managed identity, configure
repository `user.name` and `user.email`, or supply them with `git -c`.
4. Run `git commit --allow-empty -m test`. Before this fix, both
identity configuration forms fail with empty identity.

**Paperclip version or commit**

Reproduced from master commit `165b10bd9`.

**Deployment mode**

Sandbox execution. The shared launcher is also used for managed local
and SSH execution.

Related work: #13094 introduced the local-operation fallback; #13053
changes launcher discovery on Windows. Neither fixes empty identity
overrides. Related identity work in #8945 and #8946 configures worktree
authorship and does not remove these environment overrides.

## What Changed

- Stage `package.json` with `"type": "commonjs"` in the launcher
directory before the Node scripts. Keep the project's package
configuration unchanged.
- Leave inherited author and committer variables unset in the real Git
process. When credentials are absent, require explicit Git identity
configuration with `user.useConfigOnly`.
- Clear empty identity merge overrides in staged shell profiles after
environment merging. Preserve nonempty captured identity values.
- Exercise real Git commits with repository and command-line identity,
broker failures, and managed-user switching. Verify startup in ES module
and CommonJS projects, shell cleanup, and captured identity
preservation.
- Document launcher module scope and local identity behavior in the
execution GitHub identity contract.

## Verification

- Confirmed both new local-commit regression cases fail before the fix
with `fatal: empty ident name`.
- Confirmed the new ES module project regression fails before the fix
with `require is not defined in ES module scope`.
- Focused launcher and shell tests: 28 passed.
- `pnpm exec vitest run --project @paperclipai/adapter-utils --exclude
'**/dist/**'`: 1,216 passed, 11 skipped across 58 files.
- `pnpm --filter @paperclipai/adapter-utils typecheck` and `pnpm
--filter @paperclipai/adapter-utils build`: passed.
- `pnpm -r typecheck` and `pnpm build`: attempted; both stop in the
unchanged native runner because Cargo is not installed on this machine.
- Full `pnpm test:run`: started locally; stopped the duplicate run after
the complete CI suite passed. No local full-suite success is claimed.
- CI on `99ea8050e`: all 53 checks passed (2 skipped), including full
tests, typecheck, build, native runner checks, and browser checks.
- Greptile reviewed `99ea8050e`: 5/5 with no findings or unresolved
comments. GitHub reports no merge conflicts with master.
- No live sandbox or GitHub push probe performed.

## Risks

- The new package scope is confined to the run-specific launcher
directory. It does not change the project's module type, launcher names,
or credential selection.
- Without a managed identity, an explicitly configured repository author
can now create local commits. GitHub access remains subject to the
existing credential broker. Global/system Git configuration, ambient
credentials, and SSH identity remain isolated.
- Managed identity still wins over repository settings. Missing local
identity still fails instead of guessing host details.
- New or resumed executions must stage the updated launcher and shell
profiles. Existing processes retain their prior files and environment
until refreshed. No database migration or sandbox image rebuild is
required.
- Revert this change to restore the prior behavior.

## Model Used

- OpenAI GPT-6 via Codex, with code inspection, implementation, and
local test execution. The hosted model variant and context window were
not exposed.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub references)
- [x] My branch name describes the change and contains no internal
Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass (the affected adapter-utils
package)
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

doc/execution-github-identity.md

@@ -26,12 +26,23 @@ Server-side Git operations and GitHub gateway calls follow the same selection ru
 
 Managed commands disable ambient Git credential helpers, Git global/system configuration, host GitHub CLI configuration, and host SSH identity access. Per-operation GitHub CLI configuration is isolated in a writable configuration directory beneath the managed launcher directory. Missing credentials clear previous author and token values; no teammate, standing delegation, host token, or company-default user's account is substituted. Anonymous/local operations remain available where supported.
 
+Without a managed identity, local commits can use an explicitly configured
+repository identity or `git -c user.name=... -c user.email=...`. The launcher
+leaves author/committer environment variables unset and requires configured
+identity instead of guessing the host user's details. Managed shell profiles
+remove empty identity overrides after environment merging, so agents do not
+need to unset them per command. A captured managed identity still takes
+precedence over repository configuration.
+
 Remote launchers prepend their directory to the execution target's effective
 `PATH`. An explicit remote `PATH` override is preserved; otherwise Paperclip
 reads the provider's environment before staging the launcher shell files.
 This keeps legacy NVM and user-local agent installations available alongside
 newer images with system-wide CLIs. The generated shell files retain that
-combined path with managed `git` and `gh` first. Sandbox command checks use
+combined path with managed `git` and `gh` first. The launcher directory has
+its own CommonJS package scope, so the extensionless Node launchers work
+inside repositories that declare `"type": "module"` without changing the
+project's package configuration. Sandbox command checks use
 the same sanitized environment as execution, so a CLI visible only in the
 provider's default environment cannot pass the launch check. Failed path
 discovery stops startup instead of silently falling back to a minimal path.