The whole hunk
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6565The receiving Claude reads the message between tool calls during an active turn, so a running tool is never interrupted. When the receiving session is idle, Claude Code starts a new turn with the message.
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67When a message that starts a new turn mentions a file as an `@` immediately followed by its path, Claude Code [attaches that file](/docs/en/common-workflows#reference-files-and-directories) as it exists on the receiving machine, resolving a relative path from the receiving session's working directory. The receiving session's [`Read` deny rules](/docs/en/permissions#read-and-edit) apply to that file, as they do to a file you mention with `@` yourself. When such a message mentions an [MCP resource](/docs/en/mcp#use-mcp-resources) with `@`, Claude Code attaches that resource from the receiving session's MCP servers. A path written without the `@` stays plain text and attaches nothing.
67A message from another session arrives as plain text. If it mentions a file or an [MCP resource](/docs/en/mcp#use-mcp-resources) with `@`, Claude sees the mention as written and Claude Code attaches nothing, whether the message starts a new turn or arrives during one. Claude can still open a mentioned path on the receiving machine with its own tools, subject to that session's permissions. Before v2.1.251, an `@` mention in a message that started a new turn attached the file or MCP resource on the receiving side.
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69A message that Claude reads during an active turn arrives as plain text with nothing attached, even if it mentions files or MCP resources with `@`.
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7169Claude Code refuses a message in the following cases:
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7371* The message is [over the size cap](#limitations). Claude Code refuses it in the sending session, before it leaves.
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192190The preview shortens only what you see. Whether or not you expand it, Claude reads the full message.
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194Claude receives the message with the sender's name and a reply address, except for a [one-way cross-machine message](#message-sessions-on-other-machines), which carries no reply address. Beyond the name and reply address, the receiving Claude gets the message's text, never the sender's conversation history or files. An `@` mention in the text can still attach a file or MCP resource on the receiving side, as described under [Message delivery](#message-delivery).
192Claude receives the message with the sender's name and a reply address, except for a [one-way cross-machine message](#message-sessions-on-other-machines), which carries no reply address. Beyond the name and reply address, the receiving Claude gets the message's text, never the sender's conversation history or files. [Message delivery](#message-delivery) covers `@` mentions in the text.
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196194A message that a [subagent](/docs/en/sub-agents) wrote arrives under the sending session's name, with the subagent identified in the message text. A reply to it reaches that session's main conversation, not the subagent.
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