docs: document Claude Code OAuth concurrency model and external flock rationale
The external flock on ${HOME}/.claude/session.lock in lib/agent-sdk.sh
is load-bearing, not belt-and-suspenders. Claude Code internally locks
OAuth refresh via proper-lockfile.lock(claudeDir) but uses the default
sibling lockfile path (<target>.lock), which lands in /home/agent/ —
the container-local overlay, not the bind-mounted .claude/ directory.
So the internal lock is a no-op across our containers.
Documents the rationale, the empirical verification, and a decision
matrix for future containers that need to run Claude Code (notably
the chat container in #623).
Refs: #623
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docs/CLAUDE-AUTH-CONCURRENCY.md
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docs/CLAUDE-AUTH-CONCURRENCY.md
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# Claude Code OAuth Concurrency Model
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## TL;DR
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The factory runs N+1 concurrent Claude Code processes across containers
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that all share `~/.claude` via bind mount. To avoid OAuth refresh races,
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they MUST be serialized by the external `flock` on
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`${HOME}/.claude/session.lock` in `lib/agent-sdk.sh`. Claude Code's
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internal OAuth refresh lock does **not** work across containers in our
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mount layout. Do not remove the external flock without also fixing the
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lockfile placement upstream.
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## What we run
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| Container | Claude Code processes | Mount of `~/.claude` |
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|---|---|---|
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| `disinto-agents` (persistent) | polling-loop agents via `lib/agent-sdk.sh::agent_run` | `/home/johba/.claude` → `/home/agent/.claude` (rw) |
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| `disinto-edge` (persistent) | none directly — spawns transient containers via `docker/edge/dispatcher.sh` | n/a |
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| transient containers spawned by `dispatcher.sh` | one-shot `claude` per invocation | same mount, same path |
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All N+1 processes can hit the OAuth refresh window concurrently when
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the access token nears expiry.
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## The race
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OAuth access tokens are short-lived; refresh tokens rotate on each
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refresh. If two processes both POST the same refresh token to
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Anthropic's token endpoint simultaneously, only one wins — the other
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gets `invalid_grant` and the operator is forced to re-login.
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Historically this manifested as "agents losing auth, frequent re-logins",
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which is the original reason `lib/agent-sdk.sh` introduced the external
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flock. The current shape (post-#606 watchdog work) is at
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`lib/agent-sdk.sh:139,144`:
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```bash
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local lock_file="${HOME}/.claude/session.lock"
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...
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output=$(cd "$run_dir" && ( flock -w 600 9 || exit 1;
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claude_run_with_watchdog claude "${args[@]}" ) 9>"$lock_file" ...)
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```
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This serializes every `claude` invocation across every process that
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shares `${HOME}/.claude/`.
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## Why Claude Code's internal lock does not save us
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`src/utils/auth.ts:1491` (read from a leaked TS source — current as of
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April 2026) calls:
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```typescript
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release = await lockfile.lock(claudeDir)
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```
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with no `lockfilePath` option. `proper-lockfile` defaults to creating
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the lock at `<target>.lock` as a **sibling**, so for
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`claudeDir = /home/agent/.claude`, the lockfile is created at
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`/home/agent/.claude.lock`.
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`/home/agent/.claude` is bind-mounted from the host, but `/home/agent/`
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itself is part of each container's local overlay filesystem. So each
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container creates its own private `/home/agent/.claude.lock` — they
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never see each other's locks. The internal cross-process lock is a
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no-op across our containers.
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Verified empirically:
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```
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$ docker exec disinto-agents findmnt /home/agent/.claude
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TARGET SOURCE FSTYPE
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/home/agent/.claude /dev/loop15[/...rootfs/home/johba/.claude] btrfs
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$ docker exec disinto-agents findmnt /home/agent
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(blank — not a mount, container-local overlay)
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$ docker exec disinto-agents touch /home/agent/test-marker
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$ docker exec disinto-edge ls /home/agent/test-marker
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ls: cannot access '/home/agent/test-marker': No such file or directory
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```
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(Compare with `src/services/mcp/auth.ts:2097`, which does it correctly
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by passing `lockfilePath: join(claudeDir, "mcp-refresh-X.lock")` — that
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lockfile lives inside the bind-mounted directory and IS shared. The
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OAuth refresh path is an upstream oversight worth filing once we have
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bandwidth.)
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## How the external flock fixes it
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The lock file path `${HOME}/.claude/session.lock` is **inside**
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`~/.claude/`, which IS shared via the bind mount. All containers see
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the same inode and serialize correctly via `flock`. This is a
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sledgehammer (it serializes the entire `claude -p` call, not just the
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refresh window) but it works.
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## Decision matrix for new claude-using containers
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When adding a new container that runs Claude Code:
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1. **If the container is a batch / agent context** (long-running calls,
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tolerant of serialization): mount the same `~/.claude` and route
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all `claude` calls through `lib/agent-sdk.sh::agent_run` so they
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take the external flock.
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2. **If the container is interactive** (chat, REPL, anything where the
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operator is waiting on a response): do NOT join the external flock.
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Interactive starvation under the agent loop would be unusable —
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chat messages would block waiting for the current agent's
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`claude -p` call to finish, which can be minutes, and the 10-min
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`flock -w 600` would frequently expire under a busy loop. Instead,
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pick one of:
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- **Separate OAuth identity**: new `~/.claude-chat/` on the host with
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its own `claude auth login`, mounted to the new container's
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`/home/agent/.claude`. Independent refresh state.
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- **`ANTHROPIC_API_KEY` fallback**: the codebase already supports it
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in `docker/agents/entrypoint.sh:119-125`. Different billing track
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but trivial config and zero coupling to the agents' OAuth.
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3. **Never** mount the parent directory `/home/agent/` instead of just
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`.claude/` to "fix" the lockfile placement — exposes too much host
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state to the container.
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## Future fix
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The right long-term fix is upstream: file an issue against Anthropic's
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claude-code repo asking that `src/utils/auth.ts:1491` be changed to
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follow the pattern at `src/services/mcp/auth.ts:2097` and pass an
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explicit `lockfilePath` inside `claudeDir`. Once that lands and we
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upgrade, the external flock can become a fast-path no-op or be removed
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entirely.
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## See also
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- `lib/agent-sdk.sh:139,144` — the external flock
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- `docker/agents/entrypoint.sh:119-125` — the `ANTHROPIC_API_KEY` fallback
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- Issue #623 — chat container, auth strategy (informed by this doc)
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