feat: add bounded history previews across nine channels

Add shared /history parsing, read-only session access, message filtering, and bounded replies. Default to three messages, cap at five, and exclude saved history commands.

Include channel integration tests, translations, command help, and the Issue #62 implementation plan.

README.en.md

@@ -163,12 +163,13 @@ Each WhatsApp bot also has its own access mode. Existing bots migrate to **Only
 | `/workspacelist` | List workspace absolute paths that still exist on the current Harness Host. |
 | `/sessionlist [workspace number or absolute path]` | List every registered session ID and title in the selected workspace; omit the argument to use the current workspace. |
 | `/session <Session ID>` | Bind the current chat to an existing Harness session. |
+| `/history [count]` | Preview recent messages from the bound Session in a direct chat; defaults to 3, capped at 5. |
 | Interactive question | Reply with an option number, option label, or custom text; separate multiple choices with commas. |
 | Remote approval | Reply with `批准` / `拒绝` / `同意` / `不同意` / `yes` / `no`. |
 
-Example: send `/models`, then `/model 2` to switch to the second model in the list; send `/reasoninglist`, then `/reasoning 2` to switch to the current model's second reasoning effort; send `/presetlist`, then `/preset 2` to select the second Agent Preset for this bot. Other examples: `/help`, `/new`, `/status`, `/version`, `/model deepseek-official/deepseek-v4-pro max`, `/reasoning --default`, `/preset marketing-jeep`, `/preset --default`, `/steer inspect only the configuration file`, `/stop`, `/compact`, `/workspace /Users/alice/projects/my-app`, `/sessionlist 2`, `/sessionlist /Users/alice/projects/my-app`, or `/session session-id`
+Example: send `/models`, then `/model 2` to switch to the second model in the list; send `/reasoninglist`, then `/reasoning 2` to switch to the current model's second reasoning effort; send `/presetlist`, then `/preset 2` to select the second Agent Preset for this bot. Other examples: `/help`, `/new`, `/status`, `/version`, `/model deepseek-official/deepseek-v4-pro max`, `/reasoning --default`, `/preset marketing-jeep`, `/preset --default`, `/steer inspect only the configuration file`, `/stop`, `/compact`, `/workspace /Users/alice/projects/my-app`, `/sessionlist 2`, `/sessionlist /Users/alice/projects/my-app`, `/session session-id`, `/history`, or `/history 5`
 
-If the Slack desktop app has no native Slash Command registered with the same name, it intercepts messages that begin directly with `/`. Send the command with one leading space instead, for example ` /presetlist` or ` /preset 2`; the plugin command layer trims surrounding whitespace, so it executes exactly like the unspaced form.
+If the Slack desktop app has no native Slash Command registered with the same name, it intercepts messages that begin directly with `/`. Send the command with one leading space instead, for example ` /presetlist`, ` /preset 2`, ` /history`, or ` /history 10`; the plugin command layer trims surrounding whitespace, so it executes exactly like the unspaced form.
 
 ### Command details
 
@@ -194,6 +195,8 @@ If the Slack desktop app has no native Slash Command registered with the same na
 - A numeric `/sessionlist` argument uses the same freshly resolved order as `/workspacelist` at command execution time. An absolute path can also select a workspace directly, and the result echoes the resolved path.
 - `/sessionlist` includes every session registered to the selected workspace. Archived sessions are marked as archived; blank and subagent sessions are included when they belong to that workspace; sessions without a title are shown as `No title yet`. Any listed ID can be passed directly to `/session Session ID`.
 - `/session` accepts exactly one Session ID obtained from `/sessionlist`. It neither creates a session nor immediately prompts the model; later messages in the current chat continue the bound session. Regular archived sessions can be bound without being unarchived, while subagent sessions cannot be bound.
+- `/history` works identically in direct chats on all nine channels. It only reads the Session already bound to this chat: it never creates a Session, prompts the model, or interrupts running tasks or pending interactions. It returns the latest 3 messages by default. `/history N` accepts a positive integer, caps values above 5 at 5, and returns fewer when fewer are available. Zero, negative, fractional, nonnumeric, and multiple arguments show usage; commands with images or files are rejected. While collecting batch input, use `/send` or `/cancel` first.
+- A user message or a final assistant reply counts as one history item, not one turn or day. The latest N items are displayed oldest first. Tool events, reasoning, injected content, and unfinished assistant output are omitted; old attachments are not downloaded or resent. Long text is marked as truncated, with at most 3 text segments per reply and no automatic pagination. After binding a Session, send `/history` manually; binding never replays history automatically. Message text may still contain sensitive information from the original conversation, so expose the bot only to trusted users.
 - `/session` locates the session's unique workspace automatically. Binding inside the current workspace replaces only this chat's mapping. A cross-workspace binding switches the bot workspace, clears the old session mappings for all of that bot's chats, and then binds this chat, so it affects the bot's other chats. A reply already being generated may still finish.
 - Workspace switches and session bindings only clear or replace dsh-im chat mappings. They never delete, empty, or archive old Session contents; an old Session can still be listed and bound again.
 - Any user admitted by the current channel access policy can run these commands; there is no separate administrator role. Telegram Compatible mode follows the original DM and group mention/reply rules, while Safe mode admits only allowlisted private users. WhatsApp Only me accepts self-chat only, Selected contacts accepts self-chat plus allowlisted direct messages, and Open responses accepts every direct message, group messages from the linked account, and mentions or replies from other group members.