ocp/docs/adr/0007-tui-interactive-mode.md

ADR 0007 — TUI Interactive Mode (subscription-pool bridge)

Date: 2026-05-31 Status: Accepted — amended by PR-4 (entrypoint hardening) Deciders: project maintainer Authority: claude CLI v2.1.158 interactive mode — verified live on the test host that sessions launched without -p / --output-format carry cc_entrypoint=cli (subscription pool), not cc_entrypoint=sdk-cli (Agent SDK credit pool). Mechanism verified on cli.js v2.1.104; live-confirmed on v2.1.158.

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Context

On 2026-05-14 Anthropic announced (effective 2026-06-15) a billing split that routes requests by cc_entrypoint:

cc_entrypoint value	Billing pool
cli	Pro/Max subscription pool
sdk-cli	Agent SDK credit pool (~$20/mo on Pro = easily exhausted)

OCP's existing path (claude --output-format stream-json -p) sets cc_entrypoint=sdk-cli. After 2026-06-15 every OCP request will draw from the Agent SDK pool rather than the subscription.

The structural response: add an opt-in mode that drives a real interactive claude session (no -p, no --output-format), which carries cc_entrypoint=cli and therefore bills against the subscription. The response text is read from claude's native JSONL transcript instead of from stdout.

This is a personal-use A-path feature (single-user, single-subscription host). It is not a multi-tenant isolation layer.

Source-verified entrypoint mechanism (PR-4 amendment)

Claude CLI's main() calls a startup function (t$A in the compiled bundle) that sets process.env.CLAUDE_CODE_ENTRYPOINT only if unset to:

(argv has -p/--print/--init-only/--sdk-url  OR  !process.stdout.isTTY) ? "sdk-cli" : "cli"

The billing header reads cc_entrypoint = process.env.CLAUDE_CODE_ENTRYPOINT ?? "unknown". The "unknown" branch is dead code for any real main() spawn — the startup function always sets a value on unset env. The real risk is not "unknown": it is a lost TTY (e.g. stdout redirected or a non-PTY spawn) silently flipping the self-classification to "sdk-cli" and drawing from the metered pool.

cc_entrypoint is one of ~6 upstream run-mode signals. The dominant discriminator is the system-prompt identity block ("official CLI" vs "Claude Agent SDK"), which is driven by genuine interactivity (no -p, no --output-format, real PTY) and is overridable by no env var. This is the real reason the tmux/no--p approach works: the spawn is genuinely interactive, not just labelled as such.

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Decision

Add CLAUDE_TUI_MODE=true as an opt-in flag in server.mjs.

How it works

1. Each request spawns a fresh tmux session running claude --model <M> --session-id <UUID> --strict-mcp-config --disallowedTools 'mcp__*' (no -p, no --output-format).
2. The spawn result is checked immediately: if tmux new-session returns a non-zero exit status (or a falsy result), the request is aborted with tui_spawn_failed: tmux session not created before the boot sleep. This is the spawn/PTY gate — OCP must not issue a billing request without a verified interactive session.
3. The serialized prompt (from messagesToPrompt) is pasted via tmux send-keys … "$(cat file)" + a separate Enter key event.
4. The answer is read from claude's native JSONL transcript at <HOME>/.claude/projects/<encoded-cwd>/<session-id>.jsonl, polling until a turn_duration system event or the wall-clock cap (CLAUDE_TUI_WALLCLOCK_MS, default 120 s).
5. The string answer is returned to OCP's existing downstream (singleflight → cache write-back → completionResponse / streamStringAsSSE) — same contract as callClaude.
6. Streaming requests are buffered then replayed as chunked SSE (no real token streaming — deliberate; "don't build fragile features").

Billing-classifier labeling (OCP_TUI_ENTRYPOINT, PR-4)

CLAUDE_CODE_ENTRYPOINT on the spawn env is managed by resolveTuiEntrypointEnv(env, mode) (exported from lib/tui/session.mjs, pure, testable). The function always deletes any inherited value first so a stray env var from OCP's own parent process can never leak in and mislabel the billing header. Then:

OCP_TUI_ENTRYPOINT	Behaviour
cli (default)	Sets CLAUDE_CODE_ENTRYPOINT=cli deterministically — subscription-pool classification. Honest only because the spawn is a genuine interactive PTY (tmux pane, no -p, stdout not redirected, new-session verified).
auto	Deletes the key → claude self-classifies via t$A (TTY → cli). Use to observe/diagnose the real TTY-derived value.
off	Leaves the env exactly as inherited — diagnostics / honesty audit only.

Governing rule (verbatim): OCP may make a true value deterministic; it may never assert a value the spawn's real state contradicts. When it cannot make the claim true (e.g. cannot guarantee a PTY), it fails/drops the request — it does not force the signal.

This is why the spawn/PTY gate (step 2 above) is load-bearing for mode="cli": if new-session fails, there is no PTY, so asserting cli would be dishonest. Abort rather than lie.

OCP never suppresses the billing header (anti-fingerprinting: we do not mask the spawn).

2026-06-15 verification protocol

Run one quiesced canary request in TUI-mode and watch the Agent SDK credit balance (not the request header). If the balance drops, the subscription pool is unreachable via spawn. Per the constitution (ALIGNMENT.md), the response is to drop the Anthropic provider rather than escalate spoofing.

Version caveat: mechanism verified on cli.js v2.1.104 + live on v2.1.158. Re-verify after any major cli.js upgrade.

Default behaviour is unchanged

When CLAUDE_TUI_MODE is unset (the default), no code path touches callClaudeTui or runTuiTurn. upstreamCall === callClaude and streaming uses callClaudeStreaming — byte-for-byte identical to the pre-TUI code path.

Kill-switch

Unset CLAUDE_TUI_MODE (or set it to any value other than "true") → stream-json path restored immediately on next restart.

Home strategy (real-home default)

TUI_HOME = OCP_TUI_HOME || HOME (defaults to the operator's real home).

• Real-home (default, OCP_TUI_HOME unset): claude runs with the operator's own ~/.claude/ — shared credentials, existing onboarding, no OAuth fork risk. ensureTuiCwdTrusted seeds the trust record for the scratch cwd in the real ~/.claude.json (atomic write).
• Scratch-home opt-in (OCP_TUI_HOME=<path>): a dedicated HOME that symlinks ~/.claude/.credentials.json from the real home (token is never copied) and seeds a stripped ~/.claude.json (no project history, trusts only the scratch cwd). Caveat: claude rewrites .credentials.json on OAuth token refresh, replacing the symlink with a regular file — this forks the credentials. Use scratch-home only with a dedicated OAuth or for ephemeral testing.

Working directory

TUI_CWD = OCP_TUI_CWD || $HOME/.ocp-tui/work (dedicated scratch cwd). Transcripts land under <HOME>/.claude/projects/<encoded-cwd>/ — a stable, single location separate from the operator's real project histories. The directory is created automatically on first request.

MCP hard-disable

--strict-mcp-config (no --mcp-config argument) prevents account-attached managed MCP servers from connecting. Belt-and-braces: --disallowedTools 'mcp__*' blocks any MCP tool invocation even if a server were somehow loaded. Built-in tools (Bash, Read, etc.) are left enabled on the A-path (single-user, acceptable).

Session namespace

All tmux sessions use the prefix ocp-tui-. The prefix-scoped reaper (reapStaleTuiSessions) kills only ocp-tui-* sessions, never olp-tui-* or any other prefix. A stale-session cleanup runs once at OCP boot when TUI_MODE is on.

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SECURITY — PROMINENT WARNING

TUI-mode is SINGLE-USER / SINGLE-OPERATOR ONLY.

claude runs as the OCP process owner with full filesystem access regardless of HOME setting. Home selection is not user isolation. If OCP is serving multiple users or guest API keys:

• A guest prompt would run claude with the operator's filesystem access.
• An adversarial prompt could exfiltrate files, run shell commands, or exhaust the subscription.

Never enable CLAUDE_TUI_MODE=true on an OCP instance that serves untrusted callers or multiple users.

The B-path (multi-tenant isolation) requires:

1. --tools "" (no built-in tools)
2. Per-key ephemeral HOME (isolated credentials + no cross-key project pollution)
3. Sandbox runtime (e.g. @anthropic-ai/sandbox-runtime)

B-path is deferred and is not implemented in this ADR. Until B-path lands, TUI-mode must only be enabled on a personal single-user OCP.

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Observability and concurrency (PR-B amendment)

Date: 2026-06-10 Status: Accepted — amends ADR 0007. Motivation: the post-PR-A code audit, findings C-4 (P1) and C-5 (P1).

C-4 — independent concurrency bound for the TUI path

The global MAX_CONCURRENT gate lives in spawnClaudeProcess() (the -p / stream-json path). callClaudeTui() never calls spawnClaudeProcess — it calls runTuiTurn(), which cold-boots a full interactive claude inside a fresh tmux session. So the TUI path had no concurrency bound: N concurrent TUI requests spawned N simultaneous cold-boot tmux+claude processes. On a small host (e.g. a Pi 4 serving a family) a burst of ~5 is an OOM risk and also multiplies subscription rate-limit pressure.

PR-B adds an independent limiter for the TUI path (lib/tui/semaphore.mjs, TuiSemaphore):

• OCP_TUI_MAX_CONCURRENT, default 2. Rationale: a TUI turn is heavy — a per-request cold-boot of tmux+claude plus up to CLAUDE_TUI_WALLCLOCK_MS (120 s) of wallclock — so a small host cannot run many at once. 2 is the conservative default that keeps a Pi-class host alive under a family burst while still allowing some overlap. It is deliberately not the same knob as MAX_CONCURRENT (default 8): the two pools have different shapes (a stream-json spawn is cheap and fast; a TUI turn is a heavy cold-boot + long wallclock), so coupling them would mis-size one of the two paths.
• Queue, don't reject. The limiter queues (awaits a slot), mirroring the spirit of MAX_CONCURRENT — requests are not dropped on contention. To bound memory against a runaway client, the wait queue itself is capped (maxQueue, default 32× the limit); when the queue is full run() rejects with tui_queue_full, surfaced as a 503 — deterministic backpressure rather than silent OOM.
• Slot released in a finally. TuiSemaphore.run(fn) releases the slot in a finally, so any throw — PR-A's honesty gates (tui_wallclock_truncated, tui_upstream_error), a tui_paste_not_landed, or a tui_spawn_failed — can never leak a slot.

This limiter has zero effect when TUI_MODE is off: callClaudeTui is never reached, so the semaphore is never entered. The default stream-json path is untouched.

C-5 — operator-visible drift surface on /health (additive)

The tui_entrypoint_mismatch warning only reached journald. After the 2026-06-15 flip, a silent sdk-cli drift (the documented top risk in this ADR — a lost TTY flipping the self-classification to the metered Agent SDK pool) would drain metered credits invisibly. PR-B adds a tui block to the /health JSON response so an operator can poll it:

tui: {
  enabled:              <TUI_MODE>,
  entrypointMode:       <OCP_TUI_ENTRYPOINT>,   // cli | auto | off
  lastEntrypoint:       <last observed cc_entrypoint, e.g. "cli", or null>,
  entrypointMismatches: <count of cli-expected-but-got-other turns>,
  inflight:             <current concurrent TUI turns>,
  queued:               <turns waiting for a slot>,
  maxConcurrent:        <OCP_TUI_MAX_CONCURRENT>
}

lastEntrypoint is recorded and entrypointMismatches incremented inside callClaudeTui in the same mismatch branch that already emits the journald warning (via recordTuiEntrypoint). inflight / queued / maxConcurrent come from the C-4 semaphore. When TUI_MODE is off the block still appears with enabled:false (cheap, harmless) so the response shape is stable for consumers regardless of mode.

ALIGNMENT authorization for the /health change

/health is a grandfathered B.2 endpoint under ADR 0006, frozen at its v3.16.4 behaviour. ALIGNMENT.md's grandfather provision states: "Any change to the contract (request shape, response shape, semantics) of a grandfathered B.2 endpoint is treated as a new authorization request and requires either a behaviour-preserving refactor PR or its own ADR."

This amendment is that authorization. The argument:

• The change is additive: it adds one new top-level field (tui) containing only new sub-fields. No existing /health field is changed, renamed, removed, or re-typed, and no existing semantics change. Existing /health consumers (the dashboard, ocp-connect, monitoring) read the fields they already read and are unaffected — the change is behaviour-preserving for them, which is exactly the bar the grandfather provision sets for a non-ADR contract change.
• The TUI observability surface is an intrinsic part of the TUI feature whose authorizing authority is this ADR (0007), not a brand-new B.2 endpoint. We are not adding a new B.2 endpoint or a new method (which would each require their own fresh ADR under the New Class B endpoint procedure) — we are extending the response of an existing grandfathered endpoint with fields that report state owned by an ADR-0007 feature. ADR 0007 is the natural home for that authority, and this amendment records it explicitly.
• cli.js does not perform this operation — /health is OCP-owned (Class B), so no cli.js citation applies; the citation is this ADR + ADR 0006 (grandfathered B.2) per ALIGNMENT.md's Class B citation requirement.

OCP_TUI_MAX_CONCURRENT summary

Env var	Default	Meaning
OCP_TUI_MAX_CONCURRENT	2	Max concurrent interactive TUI turns. Independent of CLAUDE_MAX_CONCURRENT (the stream-json path). Excess turns queue (bounded); a full queue yields a 503.

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Consequences

Positive

• After 2026-06-15, requests in TUI-mode bill against the Pro/Max subscription pool (cc_entrypoint=cli) rather than the Agent SDK credit pool.
• Kill-switch is immediate (unset env var + restart); zero code change required.
• Default stream-json path is untouched — no regression risk for existing deployments.

Negative / trade-offs

• No token streaming: responses are buffered then replayed as chunked SSE. Clients see a delay then the full response arrives; real-time token streaming is not available in TUI-mode.
• Billing unmeasurable until 2026-06-15: the cc_entrypoint=cli signal is verified, but the credit deduction from the correct pool cannot be confirmed until the billing split activates.
• tmux dependency: the host must have tmux installed. CI / Docker images that lack tmux cannot use TUI-mode (the default stream-json path is unaffected).
• Wall-clock cap: long Opus thinking turns may hit the 120 s cap. Increase CLAUDE_TUI_WALLCLOCK_MS if needed (no quiescence heuristic — the reader polls until terminal marker or cap).
• Grey-area usage: running an interactive claude session headlessly to serve HTTP requests is not an officially documented use case. If Anthropic policy changes to block this pattern, OCP must fall back to the stream-json path (unset CLAUDE_TUI_MODE).

Coexistence

• tmux prefix ocp-tui- is registered. Any co-hosted OLP test instance must use olp-tui-. Never run two TUI proxies on the same OAuth concurrently — stop one instance during integration testing.

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Provenance

TUI-mode originated in a prototype contributed via PR #101 (see the PR for author attribution). The productionization design is in docs/superpowers/specs/2026-05-30-tui-mode-production-design.md. Spikes S1–S6 / T1–T6 were validated live on the test host against claude v2.1.158.