fix(web): say what actually went wrong instead of "unknown" (#448)

* fix(web): say what actually went wrong instead of "unknown"

Every failing endpoint returned "An error occurred; see logs for
details" and nothing else. That is survivable until the logs are the
thing you cannot reach: a device whose SD card was failing answered the
restart action, /system/status and /logs with that same sentence -- the
log viewer included, because journalctl could not be executed -- while
the exception underneath said

    [Errno 5] Input/output error: 'systemctl'

which names the fault outright. The only endpoint that helped was
/health, and only because it happens to pass a subprocess's stderr
through. Diagnosis came down to guessing which endpoint leaked something.

Add describe_exception(), returning "TypeName: message" on one line, and
populate the `details` field that the response schema has always had and
nothing ever filled. The type alone carries information -- a bare
PermissionError says more than any generic sentence.

Exception text is not automatically safe to echo: a requests error
quotes the URL it failed on, and plugins that authenticate by query
string put their key there. Credential values are redacted while the
parameter name is kept, since knowing which credential was involved is
part of the diagnosis. Length is capped and newlines collapsed so a
parser's context cannot flood a JSON field.

Nine handlers in api_v3 bound the exception and never used it, so the
promised log entry was never written either -- "see logs for details"
was false, not merely unhelpful. Those now log with a traceback and
carry the detail. The other 60 already logged and are unchanged; they
can adopt the helper as they are touched.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(web): redact auth headers and URL userinfo, and cover every handler

Three review findings.

The sanitizer missed two credential shapes that requests puts in its
exception text verbatim: `Authorization: Bearer <token>` and
`https://user:password@host`. Both would have gone straight into a
response. The auth-scheme name and the username are kept -- they say
which credential and whose without being the secret.

The AST test only asked whether *something* had been logged, so a
`logger.info("failed")` satisfied it while discarding the exception just
as completely. It now requires an error-level record carrying exc_info
and `describe_exception()` called on the handler's own bound exception.

Enforcing that revealed the first cut had scoped itself wrongly. I had
converted the nine handlers that logged nothing and left the sixty that
logged, reasoning their detail was at least in the journal. But
/system/status is one of the sixty, and on the failing device it told me
nothing -- the journal was exactly what could not be read. Splitting
them left most of the diagnostic surface unhelpful for the case this
change exists for, so all sixty-nine now carry the detail.

Two handlers had no bound exception name, and three passed the message
through a variable rather than a literal; both shapes needed doing by
hand. Full suite: 2383 passed, one pre-existing unrelated failure.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(web): stop reporting client errors as server faults

Werkzeug's HTTPExceptions subclass Exception, so the catch-all handler
saw them too and turned every 405, 400, 413 and 415 into a 500
UNKNOWN_ERROR. A GET on a POST-only route answered "an error occurred;
see logs for details", which tells the caller nothing and blames the
wrong side -- found while probing a device whose POST-only config
endpoints did exactly that.

Hand HTTPExceptions back as themselves, with their own status and
description. A genuine server fault still reports as one, with the
detail this branch adds.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

* fix(web): redact any auth scheme, and require the detail in the response

Two review findings.

The auth-header pattern listed Bearer, Basic, Digest and Token, so
`Authorization: ApiKey SECRET` or `Negotiate SECRET` went to the client
intact. A fixed list silently leaks whatever it does not name, and
plugin APIs invent their own schemes, so match any scheme name and keep
it while redacting the credential.

The AST test accepted a describe_exception(e) call anywhere in the
handler, which a handler could satisfy by computing the detail and
dropping it before returning the generic message. It now requires the
call inside every return expression, which is where it has to be to
reach the caller.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/web_interface/error_handler.py

@@ -4,6 +4,7 @@ Centralized error handling for web interface.
 Provides helpers for consistent error responses across API endpoints.
 """
 
+import re
 from typing import Any, Optional
 from flask import jsonify
 
@@ -16,6 +17,78 @@ from src.logging_config import get_logger
 logger = get_logger(__name__)
 
 
+# Credentials that turn up inside exception text. A requests error quotes the
+# URL it failed on, and plugins that authenticate by query string put their key
+# there, so echoing an exception verbatim can hand out an API key. Redact the
+# value, keep the parameter name -- knowing *which* credential was involved is
+# part of the diagnosis.
+_REDACT_CREDENTIAL = re.compile(
+    r'((?:api[_-]?key|access[_-]?token|auth|apikey|key|passwd|password|pwd|'
+    r'secret|sig|signature|token)["\']?\s*[=:]\s*["\']?)([^\s&"\'<>,}]+)',
+    re.IGNORECASE,
+)
+
+# `Authorization: <scheme> <credential>`. The scheme name is kept because it
+# says which kind of credential failed; the credential goes. Any scheme
+# matches, not a fixed list: ApiKey, Negotiate, NTLM, AWS4-HMAC-SHA256 and
+# whatever a plugin's API invents next are all credentials, and a list would
+# silently leak the ones nobody thought of. Not covered by the generic pattern
+# above, whose value part stops at whitespace and so would keep the credential
+# once a space follows the scheme.
+_REDACT_AUTH_HEADER = re.compile(
+    r'((?:proxy-)?authorization["\']?\s*[=:]\s*["\']?\s*'
+    r'(?:[A-Za-z][\w.+-]*[ \t]+)?)'          # optional scheme name, kept
+    r'([^\s,"\'<>}]+)',                       # the credential, redacted
+    re.IGNORECASE,
+)
+
+# Credentials embedded in a URL: https://user:password@host. requests quotes
+# the full URL in its exceptions, so this is a realistic leak. The username is
+# kept -- it identifies which account failed without being the secret.
+_REDACT_URL_USERINFO = re.compile(r'([a-z][a-z0-9+.-]*://[^/\s:@]+:)([^/\s@]+)(@)',
+                                  re.IGNORECASE)
+
+# Long enough for an errno string with a path, short enough not to dump a
+# parser's worth of context into a JSON field.
+_MAX_DETAIL_LENGTH = 400
+
+
+def describe_exception(exc: BaseException,
+                       max_length: int = _MAX_DETAIL_LENGTH) -> str:
+    """
+    One-line, safe-to-return description of an exception.
+
+    The generic "an error occurred; see logs for details" tells a user nothing
+    and, when the failure is bad enough, the logs are unreachable too: a device
+    whose storage was failing returned that message from every endpoint
+    *including* the log viewer, because journalctl could not be executed. The
+    underlying `[Errno 5] Input/output error` named the fault immediately.
+
+    Returns "TypeName: message", credentials redacted and length capped. The
+    type alone is worth carrying -- a bare PermissionError says more than any
+    generic sentence.
+
+    Args:
+        exc: The exception to describe
+        max_length: Truncate beyond this many characters
+
+    Returns:
+        A single-line description, never empty
+    """
+    message = str(exc).strip()
+    text = f"{type(exc).__name__}: {message}" if message else type(exc).__name__
+    # Order matters: the URL and header forms are more specific than the
+    # generic key=value pattern, which would otherwise chew the scheme.
+    text = _REDACT_URL_USERINFO.sub(r'\1<redacted>\3', text)
+    text = _REDACT_AUTH_HEADER.sub(r'\1<redacted>', text)
+    text = _REDACT_CREDENTIAL.sub(r'\1<redacted>', text)
+    # Collapse newlines/tabs so the detail stays one line in a JSON field.
+    text = ' '.join(text.split())
+    if len(text) > max_length:
+        text = text[:max_length - 1].rstrip() + '…'
+    return text
+
+
 def create_error_response(
     error_code: ErrorCode,
     message: str,