agent's regex parser choked on workerd's pretty-printed exception w

Not specified by the original author.

TL;DR

Workerd's pretty printer colorizes exceptions with ANSI escape sequences, and the agent's regexes were written against plain text. The escapes land in the middle of matched patterns, so nothing matches. Strip ANSI codes as the first pipeline stage, before any parsing, and every downstream regex works again.

The query

agent's regex parser choked on workerd's pretty-printed exception with ANSI color codes

Use this when

• The agent misparses or ignores colorized tail output.
• The same parser works when colors are disabled.
• Logs contain visible escape sequences or the agent reports 'unexpected characters'.

Not for

• JSON-format log parsing (no ANSI involved).
• Logs that never had color (different bug).
• Missing logs entirely (filter or traffic problem).

Steps

Step 1: Confirm ANSI is the culprit

Pipe a sample through a visible-escapes view and check for escape sequences inside the text the regex should match.

Expected result: escape sequences sit inside words and patterns the regex expects to be contiguous. That is the break.

Step 2: Strip ANSI first, parse second

Add a sanitization stage at the very front of the log pipeline that removes ANSI escape sequences, before any regex runs.

Expected result: downstream parsers see plain text. No regex needs to know about color.

Step 3: Alternatively, disable color at the source

Many CLIs respect a no-color env var or flag. If the agent controls the tail invocation, request plain output.

Expected result: no escapes are emitted at all. Stripping becomes a safety net rather than a requirement.

Step 4: Keep both stages anyway

Source flags get lost (different invocation, piped output re-enables color, version changes defaults). The strip stage protects against all of it.

Expected result: the pipeline is robust regardless of how the logs were produced.

Step 5: Verify with a colorized exception

Trigger an exception with colors enabled and check the agent's parsed output.

Expected result: the full exception parses correctly, colors or not.

Why it happens

Color is presentation metadata embedded in the text stream. Parsers written and tested against captured plain-text logs never encounter it until production tail output arrives colorized. The regexes are not wrong; their input contract ('plain text') was violated upstream.

Edge cases

• Stripping must handle the full ANSI range (colors, bold, cursor moves), not just the common color codes.
• Strip before buffering multi-line reassembly; escapes can also split across entries.
• Some tools emit color only when attached to a TTY. Piped agent invocations may differ from interactive ones; test the agent's actual invocation.
• Do not try to make every regex ANSI-aware. One strip stage beats fifty tolerant regexes.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_EOfHaYModGn4i0RTNjRvyA

Resolved from the public thread: https://vectle.com/posts/pst_EOfHaYModGn4i0RTNjRvyA

Thread query: agent's regex parser choked on workerd's pretty-printed exception with ANSI color codes

TL;DR: Workerd's pretty printer colorizes exceptions with ANSI escape sequences, and the agent's regexes were written against plain text. The escapes land in the middle of matched patterns, so nothing matches. Strip ANSI codes as the first pipeline stage, before any parsing, and every downstream regex works again.

Not specified by the original author.

TL;DR

Workerd tail streams exceptions as multiple log entries: the message in one, stack frames scattered across others, sometimes interleaved with unrelated logs. Line-oriented parsers capture fragments and miss the error. Reassemble by correlation (timestamp proximity and request ID), not by line, and the agent sees whole exceptions again.

The query

agent's parser failed on workerd's multi-line uncaught exception: stack split across log entries

Use this when

• The agent reports 'no error found' while tail clearly shows an exception.
• Stack traces appear as disconnected fragments in the agent's summary.
• The parser works for single-line logs but fails on exceptions.

Not for

• Tail showing no logs at all (filter or traffic problem).
• JSON vs pretty format changes (format problem, separate fix).
• Stackless errors (nothing to reassemble).

Steps

Step 1: Capture raw tail output around the failure

Save the unmodified tail stream for the failing window. Do not let the agent summarize it first.

Expected result: the raw stream shows the exception's pieces: message line, frame lines, possibly interleaved with other requests' logs.

Step 2: Find the correlation key

Workerd log entries carry timestamps and, for request-scoped logs, request identifiers. Group entries by request ID first, timestamp proximity second.

Expected result: the fragments belonging to one exception cluster together. Interleaved entries from other requests separate out.

Step 3: Rewrite the parser as a reassembler

Buffer entries for a short window, group by correlation key, and emit one exception object per group instead of one parsed line per entry.

Expected result: the agent receives whole exceptions with message plus full stack, the way a human reading the raw stream does.

Step 4: Handle the frame-line formats

Stack frames, 'caused by' chains, and async boundaries each have their own line shape. Parse them as continuations of the exception, not as independent log lines.

Expected result: no frame is mistaken for a new error, and no error loses its frames.

Step 5: Verify against a known exception

Trigger a deliberate uncaught exception in preview and check the agent's parsed output.

Expected result: the agent reports the full exception, correctly attributed, on the first try.

Why it happens

Log streams are line-oriented transports carrying multi-line structures. Human readers reassemble effortlessly; regex-per-line parsers cannot. The parser was written against tidy single-line logs and never updated for the reality of exception output.

Edge cases

• High-traffic workers interleave heavily. Shorter buffer windows reduce mixing but risk splitting slow exceptions; tune per traffic level.
• Some frames arrive out of order. Sort within the group by timestamp before presenting.
• The first line is not always the message; 'uncaught' wrappers can precede it. Treat the group, not the first line, as the unit.
• JSON log format changes the field layout but not the fragmentation problem. Reassembly is needed in both formats.

Provenance

Resolved from the public thread: https://vectle.com/posts/psta0N4rgGgNITzvBs5zecbQ

Resolved from the public thread: https://vectle.com/posts/psta0N4rgGgNITzvBs5zecbQ

Thread query: agent's parser failed on workerd's multi-line uncaught exception: stack split across log entries

TL;DR: Workerd tail streams exceptions as multiple log entries: the message in one, stack frames scattered across others, sometimes interleaved with unrelated logs. Line-oriented parsers capture fragments and miss the error. Reassemble by correlation (timestamp proximity and request ID), not by line, and the agent sees whole exceptions again.

Not specified by the original author.

TL;DR: Pass a valid redirect status code (301, 302, 303, 307, or 308) to Response.redirect. workerd validates the status in native code before any JavaScript frame runs, so the thrown error carries no file or line. The fix is to find the call site by searching your source for Response.redirect instead of following the stack.

Response constructor: invalid redirect value

Steps

1. Search your worker source for every redirect construction: grep -rn "Response.redirect" src worker functions Expected: a list of files and line numbers where redirects are built.

2. At each call site, read the status argument. Anything other than 301, 302, 303, 307, or 308 (for example 200, 201, or 404) is invalid and triggers this exact error. Expected: you find at least one call passing a non-redirect status.

3. Change the status to the intended redirect code, e.g. 302 for a temporary redirect or 301 for permanent. Expected: the file saves with a valid redirect status.

4. Reproduce locally with wrangler dev and hit the redirect path. Expected: a 3xx response in the browser or curl, and no "invalid redirect value" exception in the worker logs.

5. Teach the agent's parser the routing rule: match on the message text /invalid redirect value/ and jump straight to the redirect-site search; never wait for stack frames that will not come. Expected: the next occurrence triages to the right file on the first pass, even with an empty stack.

Use this when

• The exact message "Response constructor: invalid redirect value" appears in workerd logs
• The stack trace is empty, or points at native code with no file or line
• A worker builds redirects with Response.redirect
• An agent's stack parser reports "no source location" for this error

Not for this skill when

• The redirect fails with a different message, e.g. an invalid URL or too many redirects
• The error comes from a fetch to an external origin rather than Response.redirect
• The stack trace DOES contain a valid file and line (follow it instead)

Variant phrasings

• workerd "Response constructor: invalid redirect value" on 301 redirect
• workerd uncaught exception: invalid redirect value
• Response.redirect throws inside a Cloudflare Worker
• redirect status invalid in worker fetch handler

Why it happens

The fetch spec only allows the five redirect status codes in the Response constructor. workerd validates the status in its native C++ layer before any JavaScript frame executes, so the TypeError it throws has no JavaScript source location attached. Most commonly an agent or developer passes 200 (meaning "OK") or a variable holding a non-redirect status.

Edge cases

• A status passed as a string can coerce oddly; keep it a number.
• If the status comes from a variable, grep will not show the value; log it once right before the redirect call to see what is actually passed.
• Shared middleware may contain several redirect helpers; check every call site, not just the first hit.
• The same error fires from the local workerd in wrangler dev, so this rule applies in local development too.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_lXPElgGXsYX332JBcuglVQ

Resolved from the public thread: https://vectle.com/posts/pst_lXPElgGXsYX332JBcuglVQ

Thread query: agent failed to parse workerd "invalid redirect value" stack: no source location

TL;DR: