Date filter at the start of a query is silently ignored

A dt filter at the start of a chat query is silently ignored — the date range is never applied to the search, and the raw filter text is sent to the LLM and the embedding model as if it were part of the question.

dt>="last week" what changed in my project

The same query with the filter at the end works correctly:

what changed in my project dt>="last week"

Cause

DateFilter.defilter requires whitespace before the filter:

    def defilter(self, query):
        # remove date range filter from query
        query = re.sub(rf"\s+{self.date_regex}", " ", query)
        query = re.sub(r"\s{2,}", " ", query).strip()  # remove multiple spaces
        return query

A filter at position 0 has nothing before it, so \s+ cannot match and the substitution does nothing. get_filter_terms uses the bare date_regex with no such requirement, so the two disagree about whether a filter is present.

Measured on master (ae229ca):

Any character that isn't whitespace suppresses the removal, so (, , and start-of-query are all affected. Whitespace-separated filters mid-query and at the end work, which is why this hasn't been obvious.

A related case: with two adjacent filters, the first one's trailing space is consumed as the second one's required leading \s+, so only one is removed.

dt>="1984-01-01" dt<="1984-12-31" summarize my year
   -> defilter: 'dt>="1984-01-01" summarize my year'

Why the date range is lost

defilter_query in processor/conversation/utils.py produces the natural-language query, then routers/helpers.py:1329 recovers the filters by subtracting it from the original:

defiltered_query = defilter_query(q)
filters_in_query = q.replace(defiltered_query, "").strip()

When defilter returns the query unchanged, filters_in_query is the empty string. filters_in_query is what gets appended to each inferred search query at line 1371 and is the only thing EntryAdapters.apply_filters sees, so the date range never reaches the database query.

Measured end to end on master:

query           : 'dt>="last week" what changed in my project'
defiltered      : 'dt>="last week" what changed in my project'   <- sent to LLM + embedding model
filters_in_query: ''
date range applied by apply_filters: []                          <- filter silently dropped

query           : 'what changed in my project dt>="last week"'
defiltered      : 'what changed in my project'
filters_in_query: 'dt>="last week"'
date range applied by apply_filters: [1784563200.0, None]        <- works

So there are two user-visible effects for the same input:

1. The date filter is not applied — results come from the whole knowledge base.
2. dt>="last week" is left in the text handed to extract_questions and to embed_query, degrading the search embedding and the LLM's view of the question.

Neither is reported to the user; the query just quietly behaves as though no date filter were typed.

Expected behavior

defilter should remove every filter that get_filter_terms reports, regardless of what precedes it. Documented syntax in query-filters.md doesn't say a filter has to be preceded by other words.

Note

WordFilter.defilter has no such leading-whitespace requirement and handles all these positions correctly. FileFilter.defilter has a different problem (it doesn't strip -file:"..." at all), which is already covered by #1345 — this issue is only about DateFilter.

Environment

• master at ae229ca
• Python 3.12, dateparser per uv.lock