Guard codex_local agents from shared OpenAI key (#8272)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies.
> - The `codex_local` adapter runs local Codex CLI processes and builds
their environment from persisted agent config plus host process env.
> - A host-level `OPENAI_API_KEY` or shared Codex auth home can silently
make new agents spend through shared credentials.
> - Existing agents can be repaired manually, but new and updated agents
need a persistent guard at the agent configuration boundary.
> - This pull request isolates new and updated `codex_local` agents with
per-agent `CODEX_HOME` and an empty `OPENAI_API_KEY` override.
> - The benefit is that future agent creation or adapter updates cannot
silently fall back to shared OpenAI credentials.

## Linked Issues or Issue Description

Paperclip work item: [ZOL-5477](/ZOL/issues/ZOL-5477).

No matching GitHub issue exists, so the bug is described inline
following `.github/ISSUE_TEMPLATE/bug_report.yml`.

**Pre-submission checklist**

- [x] I have searched existing open and closed issues and this is not a
duplicate.
- [x] I am on the latest `master` commit for this PR branch.
- [x] I have confirmed the error originates in Paperclip's `codex_local`
adapter configuration boundary, not in a provider outage.

**What happened?**

New or updated `codex_local` agents could inherit a host-level
`OPENAI_API_KEY` or use a shared Codex home when their adapter config
did not explicitly isolate those values. That made it possible for
future agents or manual adapter edits to silently fall back to shared
OpenAI credentials.

**Expected behavior**

Creating, hiring, or updating a `codex_local` agent should either
persist isolated per-agent configuration or reject unsafe shared Codex
home configuration with a clear 422 response. The guard must not print
secret values.

**Steps to reproduce**

1. Create or update a `codex_local` agent without an explicit
`adapterConfig.env.OPENAI_API_KEY` override.
2. Run it on a host where the Paperclip server process has
`OPENAI_API_KEY` set.
3. Observe that the adapter process can inherit the host key unless
Paperclip persists a blocking empty override.
4. Set `adapterConfig.env.CODEX_HOME` to a shared path such as
`~/.codex` or the company-level `codex-home`.
5. Observe that the old code allowed the shared auth home instead of
returning a validation error.

**Paperclip version or commit**

- Reproduced by inspection against `master` before this PR.

**Deployment mode**

- Local dev / self-hosted server with `codex_local` agents.

**Installation method**

- Built from source.

**Agent adapter(s) involved**

- Codex.

**Database mode**

- Not database-related.

**Access context**

- Board and agent configuration paths.

**Relevant logs or output**

- No secret-bearing logs included.

**Relevant config**

- Unsafe shape: missing `adapterConfig.env.OPENAI_API_KEY`, or shared
`adapterConfig.env.CODEX_HOME`.
- Fixed shape: per-agent `CODEX_HOME` plus empty `OPENAI_API_KEY`
override.

**Additional context**

Related PR search for `codex_local OPENAI_API_KEY CODEX_HOME` found:

- #3681 `fix: preserve managed Codex auth and repo-root env loading`
- #5621 `fix: copy worktree codex auth locally`

Those are adjacent auth-handling changes, but they do not add the agent
create/update guard implemented here.

**Privacy checklist**

- [x] I have reviewed all pasted output for PII, usernames, file paths,
API keys, tokens, company names, and redacted where necessary.

## What Changed

- Added a `codex_local` config guard in agent create, hire, and update
routes.
- The guard assigns `adapterConfig.env.CODEX_HOME` to
`companies/<companyId>/agents/<agentId>/codex-home` when missing.
- The guard persists `adapterConfig.env.OPENAI_API_KEY = ""` when
missing, preventing host env inheritance.
- Shared `CODEX_HOME` values for the company codex-home, host
`$CODEX_HOME`, or `~/.codex` now fail with a 422 error.
- Added route tests for create, hire, update, and rejected shared host
Codex home.
- Updated `codex_local` and development docs to describe the per-agent
home contract.

## Verification

- `pnpm exec vitest run
server/src/__tests__/agent-adapter-validation-routes.test.ts`
- `pnpm exec vitest run
server/src/__tests__/agent-skills-routes.test.ts`
- `pnpm typecheck`
- `git diff --check upstream/master...HEAD`
- `gh pr list --repo paperclipai/paperclip --state all --search
"codex_local OPENAI_API_KEY CODEX_HOME" --limit 20 --json
number,title,state,url`
- `rg -n "codex|OPENAI_API_KEY|CODEX_HOME|adapter" ROADMAP.md` returned
no roadmap overlap.

## Risks

- Existing legacy `codex_local` agents with shared `CODEX_HOME` will get
a clear 422 when their adapter config is updated until the shared path
is replaced. This is intentional because silent fallback is the bug
being guarded.
- Low migration risk: no database migration and no secret values are
printed or persisted beyond the empty override.

## Model Used

- OpenAI GPT-5.5 Codex, Codex coding-agent session with repository tool
use.

## 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 run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [ ] All Paperclip CI gates are green
- [ ] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

## Paperclip

- Issue: [ZOL-5477](/ZOL/issues/ZOL-5477)
- Owner: Разработчик (`6625498c-66c9-429f-b578-4463ddc3ba16`)
- Status: waiting reviewer
- Next action: merge after approval and green CI

---------

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

doc/DEVELOPING.md

@@ -196,7 +196,8 @@ Every local install keeps runtime state directly under the selected instance roo
   secrets/master.key                             # local_encrypted master key
   workspaces/<agent-id>/                         # default agent workspaces
   projects/                                      # project execution workspaces
-  companies/<company-id>/codex-home/             # per-company codex_local home
+  companies/<company-id>/agents/<agent-id>/codex-home/
+                                                   # per-agent codex_local home
 ```
 
 `PAPERCLIP_HOME` and `PAPERCLIP_INSTANCE_ID` override the home root and instance id respectively. `paperclipai onboard` echoes the resolved values in its banner (`Local home: <home> | instance: <id> | config: <path>`) so you can confirm where state will land before continuing.
@@ -266,9 +267,11 @@ When a local agent run has no resolved project/session workspace, Paperclip fall
 
 This path honors `PAPERCLIP_HOME` and `PAPERCLIP_INSTANCE_ID` in non-default setups.
 
-For `codex_local`, Paperclip also manages a per-company Codex home under the instance root and seeds it from the shared Codex login/config home (`$CODEX_HOME` or `~/.codex`):
+For `codex_local`, Paperclip assigns new and updated agents an isolated Codex home under the instance root and blocks shared host/company Codex homes:
 
-- `~/.paperclip/instances/default/companies/<company-id>/codex-home`
+- `~/.paperclip/instances/default/companies/<company-id>/agents/<agent-id>/codex-home`
+
+Paperclip also persists an empty `OPENAI_API_KEY` override for those agents so a host-level `OPENAI_API_KEY` cannot leak into Codex runs through process inheritance. If an operator explicitly configures `adapterConfig.env.CODEX_HOME`, it must not point at the shared company `codex-home`, `$CODEX_HOME`, or `~/.codex`.
 
 If the `codex` CLI is not installed or not on `PATH`, `codex_local` agent runs fail at execution time with a clear adapter error. Quota polling uses a short-lived `codex app-server` subprocess: when `codex` cannot be spawned, that provider reports `ok: false` in aggregated quota results and the API server keeps running (it must not exit on a missing binary).