feat: /session command to switch to any existing session (issue #8)

[HarveyZed]

Summary

Adds a /session command that lets a Feishu conversation switch to any existing session in its workspace — including sessions created in the Web UI (dsh web). This closes the gap where a chat is permanently bound to one auto-derived session, and hardens the feature against the session-lifecycle edges the switch opened up.

Companion request: issue #8 (dsh持久化会话，应支持切换已有会话列表).

What it does

Command	Effect
/session	Card listing switchable sessions in the current workspace: title (label) + id (value) per row, so a phone user can copy the id
/session <id>	Bind this conversation to an existing persisted session (agents.resume()), continuing its context from the next message; an id that is not a session is refused instead of silently creating one
/session <title>	Bind by the title of a switchable session, mirroring how /cd accepts a directory's basename; an ambiguous title lists the candidate ids
/session reset	Clear the binding, back to automatic derivation

Fixes in this series

• Live-reuse composition: a chat reusing a live agent another owner keeps running (typically a Web UI session) never ran the create/resume setup, so the shadow registrations for ask_user_question / plan review were missing and questions fell through to the Web UI's provider. Reuse now composes the chat-only parts idempotently (WeakSet-keyed), skipping the preset join, with a try/catch so reuse never costs the message.
• /new and /cd were shadowed by an override: once bound, sessionIdForKey always prefers the override, so /new's fresh epoch (and /cd's new directory) never took effect — the next message resumed the old bound session. Both commands now clear the binding on success (/new unconditionally; /cd only when the directory actually changed, via the onSwitched callback), and /new's reply copy mentions the unbind.

Implementation notes

• Symmetric to ChatWorkspaces (/cd): a per-chat override map (ChatSessionOverrides) persisted through the settings service (chatSessions field). sessionIdForKey / releaseFor / statusFieldsFor honor the override.
• Session titles are folded via sessionQuery.readTitleSnapshots() (handles the settled-wrapper return shape). Shown in the /session card and in /status.
• Archived sessions (Web UI workspaceRegistry.archivedSessionIds) are filtered out of the list; they can still be resumed directly via /session <id>. The id-existence check runs against the FULL persisted list, so cross-directory and archived sessions stay switchable.
• Session resolution tries the argument as an id first (exact, unique), then as a title in the current workspace's switchable sessions; resolution runs before the id-format check so titles may contain any characters.
• /status gains a switched activity state ("已切换到指定会话，下一条消息接续") instead of the misleading "尚未创建".
• Card copy is bilingual (zh/en), following the existing card vocabulary.
• README command tables updated for the /session family and /new's unbind behavior (zh/en).

Verification

• tsc -b: 0 errors
• vitest run: 490 passed, 2 skipped (19 files)
• Manually tested against a live dsh 0.1.0-rc.6 + Feishu deployment: question cards from a reused live session, /new / /cd unbinding, phantom-id refusal, and title switching incl. ambiguous-title refusal.

[Roy-oss1]

Thank you for this, @HarveyZed — it shipped in v0.0.7.

Your commit is in main unchanged and under your name (918b770), as the first of the two commits in #14, and the release notes credit you at the top: https://github.com/omdsh-dev/dsh-lark/releases/tag/v0.0.7

Two parts of your work were kept as they are:

• the persisted shape — chatSessions in src/config.ts, wired through the interface, the schema and resolveConfig, symmetric to ChatWorkspaces down to the single-key patch;
• the /status surface for a switched conversation.

What changed on top, and why, in case it is useful for the next one:

• /session <id> became /sessions, a list you press. A session id is a machine identifier, and typing one is hard on the phone this channel is mostly driven from. It also opens a second way in: with a typed id, something has to decide which ids a chat may name. With a list, nothing does — the rows are derived per render, and the click handler derives the same list again rather than trusting the id in its payload.
• The switch now releases the conversation's agent. SessionStore.acquireKey hands back an already-bound agent without re-deriving the id, so without a release the switch had no effect until the agent went away on its own.
• Delegated and archived sessions are filtered out, the latter via workspaceRegistry.archivedSessionIds — your idea, and one the new picker kept.
• Rows are labelled by the last thing a person said, because a title is folded from a session's first prompt and half of them read "Hello".

The full reasoning is in #14 and in src/sessions.ts. Closing this one as superseded — the feature and your commit are both in main. Thanks again, and please do send more.