Add Claude structured session adapter

[brennanb2025]

Summary

Adds the host-side Claude structured-session adapter as the first PR in the Claude stack. It drives the user's installed Claude CLI directly through one long-lived bidirectional stream-json child per session; no Agent SDK or package dependency is added.

The adapter pre-mints deterministic provider session IDs, resumes from the durable provider-handle chain, pins CLAUDE_CONFIG_DIR, proves ownership through system/init plus process identity, buffers events until acquisition is committed, and persists the last observed leaf on graceful close. It also implements replay-acknowledged sends, acknowledged interrupt/model/permission-mode/effort controls, live model discovery with shared-catalog fallback, bounded image inputs, permission and multi-question callbacks, and fail-closed local-only capability data for SSH/WSL.

Launches deliberately use the default interactive setting sources (user,project,local) so user MCP servers, skills, hooks, project instructions, and configured auth/gateway behavior remain intact. The adapter never strips or overrides auth environment; diagnostics expose only booleans and setting-source names, never credential values or gateway URLs.

Screenshots

No visual change.

Testing

• pnpm lint
• pnpm typecheck
• pnpm test — 49,035 passed and 99 skipped; 5 unrelated baseline/environment failures remained in the macOS Bash 3 root-directory fixture, a timed macOS helper-process fixture, and the real POSIX SSH GC scale fixture. The Claude-focused suite passes independently.
• pnpm build — not run; this host-only adapter adds no packaging dependency or UI surface.
• Added high-quality tests for launch/resume identity, setting-source and account pinning, stream framing, control acknowledgements, auth-diagnostic redaction, init mismatch/startup failure, dispatch replay identity, live model discovery, prompts, and graceful leaf persistence.

Additional gates:

• Claude focused: 3 files, 18 tests passed.
• Mobile: pnpm lint, pnpm typecheck, and pnpm test passed; 451 files and 3,451 tests passed, 3 skipped.
• pnpm run check:max-lines-ratchet passed.
• pnpm run check:code-quality:changed passed with zero new findings.

AI Review Report

Reviewed acquisition races, init/session proof, chain-head resume behavior, replay acknowledgement, close persistence, prompt callback cardinality, option discovery fallback, bounded input handling, and secret exposure. The review found and fixed two issues: startup exits now reject acquisition immediately instead of waiting for the init deadline, and auth-source diagnostics were reduced to booleans rather than relaying provider strings.

Cross-platform review covered macOS, Linux, and Windows command launch semantics, including the existing Windows wrapper path and platform-native process-tree cleanup. This slice intentionally reports SSH and WSL unsupported; local folder workspaces and git worktrees share the same path resolver, and no keyboard, UI, or Electron behavior changes here.

Security Audit

• Uses an argument array and the existing Windows command wrapper; it does not compose a shell command.
• Inherits the user's existing auth lane and pins only the managed account home plus an ownership spawn token.
• Preserves interactive setting sources and never introduces an API-key flow.
• Reports only boolean auth-presence signals; token and URL values are not emitted.
• Validates and bounds local image files to 5 MiB and a fixed MIME allowlist.
• Bounds stream lines and stderr retention, serializes stdin writes, times out control requests, and fails closed on malformed output.
• Adds no dependency and no new IPC/wire opcode.

Notes

The subscription-auth product-policy decision remains parked; this PR uses the user's installed CLI and existing login exactly as approved, and does not implement around that dependency with API keys.

Deferred to the next stacked PRs: Claude event-to-journal translation plus runtime/wire registration, then opt-in capability-gated client selection and option UI. The branch is rebased on 9202192f10; later stack PRs will stay based on the current Codex structured tip, and this PR can be retargeted to the default branch after its base merges.

[brennanb2025]

Superseded: this stack part is fully contained in the consolidated big PR (#13438 for Codex, #13584 for Claude) per the two-big-PRs plan. History and review evidence preserved on this PR.