fix(agent): a session id is an address

[jaredLunde]

The bug

Every distinct session id in one directory resolved to the same session, and there was no way to ask for a new one.

SessionRepo::resume_or_create matched on cwd first and consulted the caller's id only in the no-match branch:

match self.list()?.into_iter().find(|m| m.cwd == cwd) {
    Some(meta) => self.open_id(&meta.id),   // <-- `id` never consulted
    None => { /* only here does the caller's id get used */ }
}

So once any session existed for a directory, every --session-id pointed at it was silently dropped. Everything that opens a session in repo mode went through it — a bare run, run --continue, serve with or without --session-dir — so N ids collapsed onto 1.

The rule

A session id is an address. It resolves to the session it names or to a brand-new one under exactly that name — never to some other session that merely shares the directory.

Split the API into the two things it was conflating:

open_or_create_id	open exactly this id, or mint it under exactly this id
resume_latest_or_create	this cwd's most recent session — now reached only via --continue

Precedence, identical in run and serve (serve::SessionSelect):

--session-id <id>   →  address one session (open-or-create, idempotent)
--continue          →  this cwd's most recent
neither             →  a fresh session

serve gains --continue to spell what its default used to do implicitly.

Behavior changes

• A bare run/serve starts its own session instead of reattaching. Two shells in one repo previously drove the same store, and append_new is count-keyed, so neither could observe the other's writes and the transcript interleaved. --continue is now the only implicit reattach.
• --session-id reopens an existing session rather than being ignored, making it idempotent — the right flag for a supervised serve, where --continue depends on whatever else touched the directory meanwhile.

Daemon

session_cfg rewrote every WS session into single-file mode purely to escape the cwd collapse. With ids taking precedence that workaround is unnecessary, and dropping it fixes what it cost:

• Daemon files were <id>.jsonl where the repo names <created_at>_<id>.jsonl, so find_path's _<id>.jsonl lookup couldn't see them — a daemon session appeared in list_sessions but switch_session reported it missing.
• Sessions are now durable across a full daemon restart, not just a reap: ?session_id=X reopens the real conversation.

Because the id is a routing key, new_session on an addressed session keeps it and archives the outgoing conversation into a sibling session (parent = the slot) instead of overwriting it — "start a new session" no longer doubles as "destroy the old one". Creating a genuinely new session over the daemon is a routing operation: connect with a new ?session_id=.

Known limit, documented in serve_ws's module docs: switch_session/fork/clone move this process's view while the routing key stays put, so the move isn't durable across a respawn. Re-keying was considered and rejected — two clients can share a session, and the target id may already be live, so re-keying either drags an unrelated client along or collides two threads onto one file.

Also

Exact-match id lookup compared an _<id>.jsonl suffix. Ids may legally contain _ (is_valid_session_id), so a lookup for b matched a session named a_b. Harmless while it only backed a convenience lookup; not harmless once it decides what an address resolves to. Now compares the parsed <id> component.

Tests

New crates/agent/tests/serve_session_addressing.rs (5 e2e) plus unit and run e2e coverage:

• an addressed session wins over an unrelated session in the same directory
• distinct ids in one directory are distinct sessions, each reopening its own transcript
• addressing is idempotent across restarts, with no duplicate session file
• a bare launch starts fresh while --continue reattaches
• new_session on an addressed session keeps the id and archives the old transcript
• b does not resolve onto a_b; abc does not resolve onto abcdef

Three existing tests pinned the old contract and were inverted or given --continue; serve_websocket's filename assertions now resolve by id instead, which is the assertion that actually matters.

Full beyond-ai-agent suite green locally (--no-fail-fast), clippy and dprint clean. ARCHITECTURE.md and the README document the selection rule.

🤖 Generated with Claude Code

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