[BUG] Agent loop stalls permanently when write_to_file partial streaming hits a filesystem error (EROFS/EACCES)

Problem

When the model uses write_to_file to create a file whose parent directory does not exist (or is on a read-only mount), the extension freezes mid-stream and never returns control to the agent loop. The user sees an error flash in the UI but the assistant never continues.

Error visible in logs:

Error handling partial write_to_file:
EROFS: read-only file system, mkdir '/scratch'

Context

Any user who asks the agent to write a file to a path whose root does not exist or is read-only (e.g. /scratch/foo.ts on macOS where /scratch does not exist) will hit this. The agent appears completely frozen and requires a manual abort or window reload.

Reproduction steps

Any OS/version where /scratch (or similar) does not exist
Ask the agent to write a file to /scratch/test.ts or any path whose parent directory cannot be created
The model issues a write_to_file tool call
Streaming begins, the UI shows the error EROFS: read-only file system, mkdir '/scratch'
The agent never continues -- no further tool calls, no error recovery, no completion

Expected result

The agent should surface the error as a tool result and continue the conversation (retry, use a different path, or report the failure to the user).

Actual result

The agent loop stalls permanently. userMessageContentReady is never set to true, so the task hangs waiting for a condition that can never be satisfied.

Root cause (technical)

WriteToFileTool.handlePartial() calls createDirectoriesForFile(absolutePath) (which calls fs.mkdir) without a .catch() guard. During streaming (block.partial === true), this throws EROFS.

The throw is caught by BaseTool.handle(), which calls handleError (correctly pushing a tool_result to API history) and returns. However, back in presentAssistantMessage(), the advancement gate:

if (!block.partial || cline.didRejectTool || cline.didAlreadyUseTool) {
    cline.userMessageContentReady = true   // never reached
    cline.currentStreamingContentIndex++   // never reached
}

is skipped because block.partial is still true and neither flag was set by handleError. The loop stalls.

Fix: Remove the createDirectoriesForFile block from handlePartial -- it is redundant since execute() already calls it before diffViewProvider.open(). All other tools handlePartialoverrides guard their async I/O with.catch(() => {})`; this one does not.

App Version

Reproducible on current main (confirmed by code inspection).

API Provider

Not Applicable / Other (filesystem error, provider-independent)

Drop the out-of-scope comment from the throttle test

Drop out-of-scope Stryker tooling changes

Restore the Stryker tooling files to the PR base

Split plan for this issue (recorded before any split PR opens)

PR #1066 is over the size cap: zdt split measure on its standalone delta vs its own base (72143527fd33306e5541116093c2cbf803cce9e0) gives 2025 a+d across 8 files -> HARD-OVERSHOOT (hard cap 1000). Changed executable lines 211/500 and valid mutants 116/400 are not breached and CI is green, so the split is driven by size + reviewability (maintainer p12tic on #1066: "it includes too many things at once"), not by a failing check.

Content source of record: tag pr1066-source = 46d1d218701f0ce2d675b1b315489bacb6b0f77d, base 72143527fd33306e5541116093c2cbf803cce9e0. Every unit contract pins source: { kind: "local", base: "72143527fd", head: "46d1d2187" }; no stacked unit head is used as a source.

Unit	Contract point (one provider group + one gate scope)	a+d
U1	`Task.saveClineMessages` stage semantics	173
U2	`Task.finalizePartialToolAsk()`	307
U3	`BaseTool.onParameterParseFailure()` boundary + WriteToFile override	258
U4	WriteToFileTool per-task stream state + cleanup primitives + ClineProvider disposal wiring	346
U5	`handlePartial` streaming failure capture + single-error reporting	242
U6	`execute()` error-path cleanup invariant (`finally` around `handleError`, `writeApproved`, mistake-counter order)	417 (soft cap, rationale in body)
U7	Early-return / rooignore-denial cleanup branches	233

Merge order (dependency-forced): U1 -> U2 -> U4 -> U5 -> U3 -> U6 -> U7 -> final integration PR (base = main, head = U7). Mid PRs base on the previous unit's head; the final PR is the sole merge target.

Cross-unit symbol ownership: U4 owns getTaskPartialStreamState, getPartialStreamFailureKey, resetTaskPartialState, clearTaskState, finalizePartialToolAskAfterFailure, revertDiffChangesBeforeReset, resetDiffViewAfterWrite; U3/U5/U6/U7 call them and rebase-and-drop their copies.

Accepted mechanism divergence (recorded decision): U4 keeps per-task keying only in WriteToFileTool while the sibling streaming tools (ApplyDiffTool, EditFileTool, SearchReplaceTool, EditTool) use BaseTool's singleton lastSeenPartialPath/resetPartialState. Lifting it into BaseTool for all streaming tools is a separate follow-up PR.

Sanctioned new content: presentAssistantMessage-custom-tool.spec.ts (+1 mock line, no source change) is listed in U2's allowNew.

Every split PR cites this issue.

Split execution status (units opened in upstream, one issue per unit)

Merge order is fixed: U12 -> U4 -> U5 -> U3 -> U6 -> U7/FINAL. The FINAL integration PR is the sole merge target; the chain PRs are review units.

Unit	Contract point	PR (upstream)	Own issue	a+d	Files	zdt split verify	Unit tests	Changed-line coverage
U12	saveClineMessages stage semantics + finalizePartialToolAsk()	#1927	#1933	481	3	PASS	218 passed / 5 skipped	18/0 PASS
U4	per-task partial stream state + cleanup primitives + provider disposal wiring	#1929	#1934	428	5	PASS	230 passed / 5 skipped	34/0 PASS
U5	streaming failure captured once, reported once	#1930	#1935	283	2	PASS	239 passed / 5 skipped	13/0 PASS
U3	BaseTool.onParameterParseFailure() teardown boundary	#1931	#1936	253	3	PASS	243 passed / 5 skipped	20/0 PASS
U6	execute() error-path cleanup invariant	#1932	#1937	439	2	PASS	259 passed / 5 skipped	14/0 PASS
U7 / FINAL	early-return + rooignore-denial cleanup; integration of the series	#1928	#1938	241	2	PASS	264 passed / 5 skipped	12/0 PASS

Content source of record: tag pr1066-source = 46d1d218701f0ce2d675b1b315489bacb6b0f77d. The final head is byte-identical to it for all 8 original files; the only additions are two sanctioned allowNew test files.

Deviations from the original plan

U1 + U2 merged into U12 — the stage-semantics tests call finalizePartialToolAsk(), so the test blocks cannot be split without orphaning them (test-block atomicity).
reports a filesystem error only once across the streaming and execute phases re-attributed from U5 to U6 — it depends on the execute() error-path restructure.
U4 gained a focused cleanup spec (src/core/tools/__tests__/writeToFileTool-partial-state-cleanup.spec.ts, +100 lines, allowNew): the primitives' catch arms are only reachable by calling them directly at this layer, so the changed-line coverage item can pass by once on U4 itself.
Chain PRs are opened against main because the split branches live on the fork (no push access upstream). GitHub therefore shows a cumulative diff for each chain PR; the unit's own delta is stated in each body. Merge strictly in order.

Not yet done

Local Stryker preflight cannot run on this Windows worktree (src/node_modules/.bin/vitest is a WSL #!/bin/sh shim, so Stryker's spawnSync gets ENOENT). CI's mutation-diff job is the authoritative gate: 211 changed executable lines / 500 cap, 116 valid mutants / 400 cap — both under the caps, no directive added.
Two stale CodeRabbit threads on fix(write-to-file): address partial filesystem error review #1066 point at src/core/task/__tests__/Task.throttle.test.ts, a file dropped in eef03b577; they need a reply/resolve on the original PR.

Per-unit issues now carry the full unit record (contract point, why the unit exists on its own, boundary, per-file a+d, budget, mutation-gate numbers, verification, deviations, reproduce commands):

U12 -> [split-1066] U12(1+2) - task save-stage semantics + finalize open partial tool ask #1933
U4 -> [split-1066] U4 - feat(write-to-file): per-task partial stream state + cleanup primitives #1934
U5 -> [split-1066] U5 - fix(write-to-file): capture the streaming failure once and report it once #1935
U3 -> [split-1066] U3 - feat(tools): onParameterParseFailure teardown boundary #1936
U6 -> [split-1066] U6 - fix(write-to-file): run the diff cleanup when handleError rejects #1937
U7 / FINAL -> [split-1066] U7 - fix(write-to-file): clean partial state on missing-param and rooignore denial #1938

Changed executable lines per unit (mutation gate, extension package, cap 500):

Unit	changed executable lines
U12	41
U4	63 (58 WriteToFileTool + 5 ClineProvider)
U5	24
U3	30 (15 BaseTool + 15 WriteToFileTool)
U6	34
U7	24

Sum 216; the whole PR measures 211 against the same gate, and valid mutants are 116 / 400 — no directive added by any unit. Each PR body now names its own issue, and each issue names its PR.

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[BUG] Agent loop stalls permanently when write_to_file partial streaming hits a filesystem error (EROFS/EACCES) #703

Problem

Context

Reproduction steps

Expected result

Actual result

Root cause (technical)

App Version

API Provider

Split plan for this issue (recorded before any split PR opens)

Split execution status (units opened in upstream, one issue per unit)

Deviations from the original plan

Not yet done

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[BUG] Agent loop stalls permanently when write_to_file partial streaming hits a filesystem error (EROFS/EACCES) #703

Description

Problem

Context

Reproduction steps

Expected result

Actual result

Root cause (technical)

App Version

API Provider

Activity

easonLiangWorldedtech commented on Oct 5, 2026

Split plan for this issue (recorded before any split PR opens)

easonLiangWorldedtech commented on Oct 5, 2026

Split execution status (units opened in upstream, one issue per unit)

Deviations from the original plan

Not yet done

easonLiangWorldedtech commented on Oct 5, 2026

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