### Readability Fallback

`readability.py` caches the optional Readability.js availability probe. If the
Node extractor is unavailable, its probe raises, or an attempted extraction
cannot launch Node, subsequent calls in that process use readabilipy's Python
fallback without retrying Node. A non-zero Node exit can be document-specific,
so it falls back only for that document and later documents retry Node. If a
future readabilipy version removes the private availability probe, log that
once at import and attempt extraction instead of silently disabling Node. Keep
successful Node extraction unchanged and allow unexpected parser/programming
exceptions to propagate. The resolved-body fallback preserves article links
when Python extraction returns the original document wrapper. Regression
coverage lives in `tests/test_readability.py` and
`tests/test_web_fetch_relative_links.py`.

### Atomic Byte Publication

`atomic_write.publish_bytes_atomically` owns browser screenshot and Browserless
capture/fetch publication. It writes and fsyncs a hidden exclusive sibling before
`os.replace`, cleaning it on failure. New files use `0666` filtered by the host
umask; replacements preserve existing permission bits before publication. Never
read the process umask by changing it in this threaded runtime. Behavioral tests
for both tool imports live in `tests/test_browser_outputs_atomic.py`.
`cleanup_failed_atomic_write` shares best-effort cleanup across this publisher,
`skills/projection.py`'s private manifest writer, project document staging,
extension snapshot rollback (including removal of a file that did not exist),
the managed plugins-block rewrite, custom-skill file writes, per-user
skill-state writes, Gateway upload staging, and the Gateway skill-archive
upload copy and its post-install discard. The upload route discards that
archive before closing the multipart form and suppresses close errors.
Use it on publication failure or after deciding to discard an owned
temporary; pass a raw descriptor only until `fdopen` succeeds, or an explicitly
transferred duplicate descriptor owned by the cleanup caller. Shelf discards
must preserve both a rejected project's 404 and a dedup hit's 200 response.
Callers retain their own serialization, permissions and publication policy.
Shelf `stage_document_bytes` drains preparation, writes, close and failure
cleanup before propagating cancellation. Retain the opened handle across its
handoff, but leave waiting for incoming chunks cancellable; regressions in
`tests/test_project_document_staging_cancellation.py` cover both shelf entry points.
Local Linux/macOS text revisions opt into a short `temporary_prefix` and
`preserve_metadata_from` (a caller-owned descriptor). Staging starts at `0600`;
`file_revision_metadata` transfers ownership, mode, ACLs and xattrs before data.
macOS uses native descriptor ACL APIs and `fcopyfile(COPYFILE_XATTR)`; Linux uses
descriptor xattrs, including its access ACL, removing inherited extras. Errors
abort; never ignore metadata permission failures. Refuse set-id bits, macOS file
flags and content-bound privilege attributes rather than reattach stale privileges to new
content. Other publisher callers retain their existing mode-only contract.
Do not restore old timestamps on a content revision, including an empty save.
Source-descriptor close failures are best-effort warnings, not save failures;
guard diagnostics so the publication result or original interruption survives.
Failure cleanup must preserve the original publication exception, including
interruptions. Descriptor close and sibling unlink are separate best-effort
operations: a close failure must not prevent the unlink attempt.
Attempt warning logs for cleanup `OSError`s with the temporary path and exception
details. Guard logging-handler exceptions so diagnostics neither replace the
publication exception (including interruptions) nor skip remaining cleanup.
Both tools take collision names from `output_names.output_name_candidates`
(name, `-1`..`-1000`, five timestamps); claim each atomically, never pre-check.

### Model Retry Hints

`retry_after.py::bounded_retry_after_ms` shares the 24-hour provider-hint ceiling
between LLM middleware (numeric/date hints) and Claude backoff. Non-finite or
over-limit delays return `None` for local backoff; finite negatives clamp to zero.
Validate before integer truncation and preserve valid hints above the jitter cap.

### Port Allocation Bounds

`network.py::PortAllocator.allocate` caps its exclusive search endpoint at
65536. A valid start near 65535 must report exhaustion with `RuntimeError`
when all remaining ports are reserved or occupied, without probing invalid
TCP ports. Keep the last valid port allocatable and preserve `max_range`.
Regression coverage lives in `tests/test_port_allocator_bounds.py`.

### Goal Objective Validation

`goal_objective.py` owns the dependency-free normalized 4000-character objective
validation shared by runtime and scheduled-task capability/repository admission.
`runtime.goal` re-exports the helper for compatibility. Validation does not replace
the saved original text; blank or over-limit text is rejected before persistence.

### Message Text Extraction

`message_content_to_text` takes raw message content and treats `None` as empty
text so downstream empty-result, error-detail, and archive-skip fallbacks work.
Keep its other conversions unchanged, including newline-separated list blocks
and literal strings such as `"None"`. Do not replace it with `message_to_text`,
which takes a whole message and uses different list/mapping semantics.
Regression coverage lives in `tests/test_utils_messages.py`,
`tests/test_subagent_executor.py`, and `tests/test_task_continuity.py`.

`llm_text.py::extract_response_text` ignores content blocks with non-string
`type` values, including lists and mappings, while retaining adjacent text and
output-text blocks. Tests cover extraction and the one-shot input-polish path
with real LangChain messages in `tests/test_utils_llm_text.py` and
`tests/test_input_polish_router.py`.

`llm_text.py::strip_think_blocks` scans opening and closing tags forward so
repeated unclosed `<think>` prefixes in model output do not rescan the same
suffix. Keep its case-insensitive tag handling, optional whitespace before
the closing `>`, and the `truncate_unclosed` behavior. Regression coverage
lives in `tests/test_utils_llm_text.py`.

Opening reasoning tags require whitespace, `>`, or `/>` after the exact `think`
name; punctuated names such as `<think-tank>`, `<think:note>`, and `<think/other>`
are ordinary content. The shared prefix regex owns this boundary rule; do not
duplicate it in a manual re-check. Self-closing `<think/>` and `<think />` tags
are empty reasoning blocks: remove the tag without consuming subsequent text.
Both cleanup functions find opening delimiters outside quoted attributes; a
quoted `>` cannot terminate the tag or hide an answer after a self-closing tag.
Keep exact unfinished `<think` prefixes hidden in leading summaries. Coverage:
`tests/test_think_tag_boundaries.py`.

Display summaries use `strip_leading_think_blocks` before limiting text;
`test_run_journal_visible_summary.py` preserves literal tags in the answer.

### Agent / Tool Assembly Off-Load

One-shot input-polish, follow-up-suggestion, and project-file-summary helpers
build providers through `run_assembly` before awaiting inference. Provider
construction can read local credentials; keep it off the event loop and the
default executor while preserving request context. Cancellation during
construction must not start inference. This contract covers callers of
`oneshot_llm.py`; standalone skill-moderation and goal-evaluator constructors
are separate sites and are not covered by this offload.
Coverage: `tests/blocking_io/test_oneshot_llm_offloop.py`.

`start_run` also resolves the factory through `run_assembly` before admission:
cold imports cannot occupy the loop or its default pool, and import errors
cannot admit a run. `tests/blocking_io/test_agent_factory_resolve_offloop.py`
pins offload, executor isolation, request context, and failure ordering.

Tool and agent assembly re-enters `get_available_tools()` and may block on MCP discovery, so the four async assembly entry points — `run_agent`'s `agent_factory` call, `task_tool`, durable batch `_execute_item`, and `abuild_checkpoint_state_accessor` — dispatch through `deerflow.utils.assembly_io.run_assembly`, a dedicated ContextVar-preserving bounded executor (`DEER_FLOW_ASSEMBLY_WORKERS`, default 8) rather than the loop's default executor; a hung MCP server therefore parks an assembly worker instead of queueing unrelated default-executor work, and the pool logs a warning when pending assemblies exceed the worker count. `tests/blocking_io/test_tool_assembly_offloop.py` pins all four offloads plus the ContextVar propagation.

### Uploaded Document Summaries

Outlines skip root-level HTML comment blocks (`<!--` with up to three leading
spaces through the first `-->` line). Comment contents cannot open code fences;
comment markers inside fenced code cannot open comment blocks. Keep line numbers
and limits unchanged. Coverage: `tests/test_file_outline_html_comments.py`.

`file_outline.py` reads outlines and fallback previews as `utf-8-sig` so an
optional leading UTF-8 BOM cannot hide a first-line heading or code fence, or
occupy a preview line. Preserve physical line numbers, embedded U+FEFF
characters, and the original file bytes.

All outline heading styles skip root-level indented code (four leading spaces
or a tab after up to three spaces), including PDF-style single and split bold
headings. Keep legitimate bold headings with up to three spaces and the shared
conversion-companion path working. Regression coverage lives in
`tests/test_file_outline_indented_bold.py`.

Split-bold headings reject numeric/punctuation/currency-only blocks after the
section number, including parentheses, signs, leading whitespace, and `$€£¥`.
Apply the check to the second through fourth blocks; preserve the four-block
limit, punctuated titles containing text, and non-ASCII titles. Coverage lives
in `tests/test_file_outline_split_bold.py`.

### Active Content MIME Types

`text_detection.py::_is_active_content_mime_type` is the shared download-safety
boundary for artifacts and project documents. Keep platform aliases such as
Windows' `image/svg` aligned with their standard active type (`image/svg+xml`),
and preserve the generic `+xml` rule.

### Conversion Worker Ownership

`convert_file_to_markdown` offloads parsing for every source size: compressed
Office files can require seconds of work below 1 MiB. It drains conversion workers
across caller cancellation before returning control to source-file cleanup. Keep conversion
inside `await_drained`, including when the worker fails or cancellation repeats;
upload ingestion owns a temporary source that it removes in `finally`. Coverage
lives in `tests/test_file_conversion_cancellation.py`.

### Host Path Portability

`host_paths.extended_length_path()` provides lexical Windows filesystem
spelling (absolute `\\?\` drive paths or `\\?\UNC\` shares); it is a no-op
on POSIX. It does not replace symlink resolution or confinement checks and
must not be used for persisted relative paths or Docker mount sources.
Existing extended (`\\?\`) and device (`\\.\`, including named pipes)
namespaces pass through unchanged before normalization.

`host_paths.py` rejects Windows device names for host-visible creation paths on
every platform, including the `COM`/`LPT` aliases with superscript ¹, ² and ³.
The console aliases `CONIN$` and `CONOUT$` are reserved too; match them
case-insensitively before the first dot, without rejecting longer ordinary
names such as `CONIN$notes.txt`.
Device-name comparison ignores ASCII spaces before the first dot, so
`NUL .txt` and `COM1  .log` remain reserved. Trim the comparison stem only,
not the supplied filename; ordinary names such as `report .txt` and
non-ASCII whitespace remain unchanged.
Do not normalize arbitrary Unicode digits into device numbers: names such as
`COM⁴.txt` and `COM¹notes.txt` are ordinary portable names. Read/removal callers
retain their existing portability exemptions.

### Advisory File Lock Retries

`file_lock.retry_until_locked` owns contention-only acquisition retries for the
Windows Lark, extension-manager and channel runtime-config locks and bounded
skill-projection reads.
Retry only EACCES/EAGAIN/EDEADLK; other errors propagate without sleeping.
Keep per-caller policies: Lark has a 15-minute Windows file-lock deadline,
extension management and channel runtime config wait indefinitely, and skill
export retains its existing deadline, 0.02-second cadence and cancellation
check. Clocks and sleeps are injectable; tests must not patch the shared stdlib
time module.
The channel caller wraps its injected sleep to warn once after 50 contention
retries; the helper remains responsible for error classification and cadence.

`parse_retry_after_date_ms(raw, now=...)` owns HTTP-date parsing for Claude, Codex
and LLM error middleware. Interpret timezone-less asctime as UTC and apply the
shared delay bound. Callers retain numeric/header precedence and local backoff.