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0041 Large code_mode results are saved

Date: 2026-10-08

Status

Accepted 2026-10-08. There is no 16 KB gate. Text is not dropped at 1 MiB. Image, audio, and blob payloads still use the 1 MiB budget from 0040.

Context

code_mode runs a C# body in the Daemon. The model is supposed to receive a small projection. A host query can still return a full element table as one string. Under 1 MiB the Daemon sends that string whole. Over 1 MiB the Daemon drops it. MCP does not require a client to keep a second copy.

Pi, releases 0.99.2 through 1.1.0, does keep a second copy, and only on the machine running Pi. output-files.ts writes every such file to the OS temp directory, mode 0600, with a random name and wx so it will not follow a planted link. The model is told to open that path with Pi's read tool. Three paths, three budgets:

What the model called View the model sees Full copy
bash, and the display of read / grep / find / ls Last 50 KB or 2_000 lines for bash. OutputAccumulator streams the bytes to disk once the view cap is passed. full_output_path on the tool result. A codemode script that calls bash receives up to 1 MiB, then head and tail of 512 KiB, with the same path.
An MCP tool, directly limitMcpContent keeps 20 KB, start and end, Codex-style. pi-mcp-*.txt. The script value is separate: Pi wraps every MCP tool in an output schema, and toScriptValue returns structuredContent, which is the original CallToolResult, not the 20 KB text.
A codemode script's own output max_output_tokens 10_000, at 4 characters per token. Start and end. pi-codemode-*.txt. The Snowdon dump (about 20_963 tokens, one line) was this file. Head and tail of one JSON line are not records, and a line offset does not split that line.

A script dies at 16 Mi characters or 100_000 text(), image(), and console calls. store() is a different mechanism: small JSON kept on the session branch, 256 KiB per value and 1 MiB total, for ids and cursors. image() uses the same temp-file helper so a later turn can move the bytes. The codemode description stays short and does not list deferred MCP tools. 0040 already follows that shape.

The half worth copying is the split: a bounded view, a complete retained copy, and a later read that does not put the copy back into the prompt. The file path does not travel. It exists only if that client writes it, the model has a file reader, and the reader runs on that same machine. A client that only renders CallToolResult has none of those. A cloud model cannot open %TEMP%\pi-mcp-*.txt.

The Daemon covers that split for every client. The model is not the component that reduces a dump, and the client is not the component that keeps it. Counting, schema, and retention are mechanical. The model keeps the questions that are actually uncertain: which slice matters, whether the live model has moved, what an outlier means.

Decision

1. The Daemon keeps the full text and returns the start, the end, and the path

There is no 1 MiB drop for text, and no 16 KB gate. When the text of a code_mode return exceeds 40_000 characters, the Daemon writes that text to a file and returns the start, the end, and the path. The file holds the full text. Structured JSON on a returned CallToolResult counts as that text.

40_000 characters is Pi's codemode view: max_output_tokens 10_000 at 4 characters per token. The return keeps 20_000 characters from the start and 20_000 from the end, then one line [Full output: path]. A return at or under 40_000 characters is sent as it is.

A return that is only image, audio, or blob still uses the 1 MiB budget from 0040 and is not saved.

The file is %TEMP%\RevitDevTool-{pid}-{id}.txt, flat in the temp directory. One save is one file. The pid keeps two Daemons apart. The file is created with create-new so an existing name is not overwritten. After the process exits, Windows removes the unused file: SilentCleanup (cleanmgr.exe) runs daily with Automatic Maintenance and deletes %TEMP% entries whose last access is older than 7 days, and Storage Sense deletes temporary files that are not in use. The Daemon does not scan the temp directory.

One saved file is capped at 64 MB. The files this process owns are capped at 256 MB. A save that would pass either cap returns an error and does not leave that file.

2. The model reads the path when the start and end are not enough

The saved call still has no outputSchema and does not set StructuredContent. The text block is the start, the end, and the path. Image and audio blocks on the same return stay with that text. A host tool answers a question about the live model. The file answers a question about this return.

Alternatives Considered

  1. Keep the 1 MiB error and drop the payload. Rejected. The rows already paid for are lost, and a client that never received them cannot save them.
  2. Send any text under 1 MiB and let the client truncate. Rejected. That is the gate this decision removes. Pi would cut it; another client may cut it with no retained copy.
  3. Save at 16 KB, or return a truncated prefix. Rejected. 16 KB is not Pi's view. A prefix is not a summary.
  4. Copy Pi store() for the element table. Rejected. The cap is 256 KiB per value and 1 MiB total, and Pi reserves it for small state.
  5. Gzip or a second summarizer model. Rejected. The model cannot read compressed bytes, and counts must come from code.
  6. Let the host script pick a path and call File itself. Rejected. The Daemon owns the file and the path.
  7. Hide the path and return only a summary. Rejected. Pi returns the start, the end, and the path of the full text. The model uses that path when the view is not enough.

Consequences

Positive:

  • Every client gets a retained copy once the text passes the view, not only Pi.
  • The model sees the start, the end, and the path of the full text.
  • A short return, at or under 40_000 characters, is sent as it is.
  • Revit is not held open while the model decides the next question.

Tradeoffs:

  • The file stays until Windows temp cleanup removes it. A later Daemon does not revive that return.
  • The host query still materializes its result before code_mode returns. Saving it keeps the model context small. It does not reduce Revit memory during the query.
  • A CallToolResult whose text exceeds 40_000 characters saves that text. Image and audio blocks on that same result are not copied into the file.
  • Image, audio, and blob results still drop at 1 MiB. That budget is not this split.
  • code_mode's description and 0040's quoted description must mention the path when this lands. Product behavior is updated in docs/product/mcp.md in that same change.

Follow-Up