Module prompt 

Turning a message’s attachments into what the agent receives (docs/specs/SPEC_AGENT_PANE_IMAGE_ATTACHMENTS_2026_09_26.md §6.6, SPEC_AGENT_PANE_FILE_ATTACHMENTS_2026_09_26.md §7):

• every provider gets a numbered list appended to the text, in an <attached_files> block: each image’s send-copy, each other file as a copy under its real name, plus notes (type, pages, text version), so any agent that can open a local file can reach every attachment;
• Claude (stream-json) additionally gets images inline as image blocks and PDFs of up to 100 pages as document blocks, within a count and size budget.

The block is also how the pane rebuilds the tiles on reload: each line names the attachment and ends with a path that carries the attachment id (a <sha256>. file name or a named/<sha256>/ folder).

Structs

Prepared

Everything a turn needs from its attachments.

Resolved

One attachment resolved to the file the agent gets.

Constants

BLOCK_CLOSE

BLOCK_OPEN

DEFAULT_INLINE_MAX_COUNT

DEFAULT_SESSION_INLINE_MB

Inline at most this much base64 across one Claude session. Claude Code keeps every inline image in its own session transcript.

INLINE_MAX_B64_BYTES

Inline at most this many base64 bytes in one Claude message. The API caps a request at 32 MB, and the whole conversation is resent each turn.

INLINE_PDF_MAX_PAGES

Claude’s PDF support takes at most 100 pages per request on models with less than a 1M-token context; longer PDFs go by path and text version.

Functions

append

The user’s text with the attachment list after it.

claude_user_line

A Claude stream-json user line. With no images, content is the plain string it always was; with images, the image blocks come first and the text last, as the Messages API recommends.

clean_name 🔒

Names go into a one-line list entry; keep them on one line and short.

inline_bytes

Base64 bytes carried by inline blocks, for the session budget.

list_block

The <attached_files> block. inlined holds the numbers of the items Claude was also given inline.

number_list 🔒

“1–3”, “2, 4 and 5”, “1 and 2”: runs of three or more consecutive numbers collapse to a range.

persisted_line

The form of a Claude stdin line that AgentMux stores for replay: image blocks dropped and the content collapsed back to its text, which still holds the <attached_images> list. Every reader of stored user lines expects content to be a string, and a stored line should never carry megabytes of base64. Lines without an array content pass through.

prepare

Build the list and (when inline_max_count > 0) the inline blocks, using at most inline_budget base64 bytes (further capped at INLINE_MAX_B64_BYTES per message). Reads the inlined files from disk. Blocking.

resolve

Resolve refs to what the agent gets. Refs whose files are gone (swept, or never finished processing) come back as names in the second list. Blocking.