[barelyworkingcode]

Closes #528

Host Claude sessions now run under one file-channel runner by default on Unix hosts. A dropped ssh link or a relay restart no longer ends the agent.

• internal/sessions/runner/runner.sh: one POSIX sh runner. It speaks the owner's agent tool protocol (inbox/ tmp-then-rename, name-order delivery, the move to sent/ is the receipt) and replaces relay's own in.jsonl runner. It writes out.jsonl unchanged and one events.jsonl line per state change (turn_started, turn_ended, asking, exited), each before its cause.
• hosts[].detach_sessions absent or true runs the runner; false and Windows hosts use ssh -T. A runner that fails to start ends the start with an error; relay never falls back on its own.
• A live run from the old layout is stopped at its first resume, after the start-time check, and resumes on its conversation.
• relay#538 (found while working this issue): the ssh ControlPath budget now counts ssh's 17-byte bind suffix. A stack's config dir is long enough that no host session started, which blocked the journey on a --stack run.
• session-detached-host moves to the api phase, drops its detach_sessions edit, and runs claude against the stack's local model endpoint through a launcher. Off a stack it reports NOTRUN; no journey calls a hosted model.

Split: local restart survival is relay#536, codex and pi are relay#537 (story unchanged).

Contract amendments (logged on the issue): internal/sessions/hostapi/server.go error text; internal/sshhost/sshhost.go budget and its docs/ssh-hosts.md sentence.

Fix attempts: legacy stop 1; review round 1 fixes 1; mawk test reach 1; journey wait signal 1 (it dropped the link on the host's receipt, before relay held it, and got a correct send_unknown once; it now drops after relay session send returns). Tokens: about 1.6M across subagents.

Minor review notes, not fixed:

• TestHostRunnerWithoutTmux also matches the outside-sessions probe's tmux list-panes; it passes because the probe's next call lands after the test window. Theoretical flake.

• docs/testing.md does not yet list mawk as a prerequisite for the e2e suite.

• runner.sh probes awk -W version relying on the launcher's closed stdin.

• G11.13 names the start-failure text, which no test asserts; TestHostSessionSSHFallbackWhenDetachOff cannot see the -T flag.

• Journey: session wait runs without --timeout, so a slow turn fails as a killed CLI rather than relay's timeout state.

Why no feature row moved beyond G11.13, G11.14, G1.40 and new G1.48: those are the rows the runner touches.

Run report: barelyworkingcode/claude-process#79

Review: no blocking findings (round 2 on 44520b2; the journey fix b684ccc reviewed separately, no blocking)
Journey: session-detached-host PASS on 3 consecutive --stack runs at b684ccc, each SUMMARY pass=6 fail=0 blocked=0 notrun=2
Real-app check: PASS at 44520b2 on a stack built from the head: a loopback host session with no detach_sessions kept runner pid 48414 through relay host disconnect; the 200-line turn finished; session events showed each line once; a second message answered on g1 with no resume
Harness weakening: no assertion removed or loosened; one not-run path widened: session-detached-host reports NOTRUN off a stack so no journey calls a hosted model (reported as a gate change)
Main harness vs head: epic base harness (121e6b8) against head 44520b2 on a stack: SUMMARY pass=5 fail=0 blocked=0 notrun=2; product code unchanged since
Break-and-restore: runner moving the message to sent/ before the write turned TestRunnerSendReturnsAfterReceipt red at its receipt assertion; restored byte for byte, green. Dropping -W interactive turned TestHostRunnerLinesFlowUnderMawk red

🤖 Generated with Claude Code

[barelyworkingcode]

Full e2e suite at 44520b2: one failure, TestFeatureMapCoverage (the new mawk test had no feature row). b8 adds it to G11.13; TestFeatureMapCoverage now passes. Every other feature test passed (586s). The fix touches only docs/FEATURES.md.

[barelyworkingcode]

merge-check: merged. approved, target, contract, evidence, owner
Report: 2. The gates themselves: skip marker added result{id, stateNotRun (cmd/devboxverify/journey_detached_host.go) [name-based]; 2. The gates themselves: criterion removed A headless local session survives a relay restart. (issue #528); 2. The gates themselves: criterion removed Claude, codex and pi sessions run under the same runner. (issue #528)