feat(inbox): point every concept at the document it came from, with a locator per format

A concept named its source file by basename and, when segmented, carried a
`source_offset` into the text THIS LIBRARY extracted. Following that pointer
needed the corpus directory, the extractor and its exact transitive version --
none of which the bundle carries. Hand-walked on a real K2 concept: six steps,
four of them requiring knowledge from outside the bundle, to learn that a
requirement sits on pages 12-13 of a 20-page document.

The address is spec's: `sources: [{ resource, title }]`, where `resource` is
the dropped file's inbox-relative path (SPEC v0.2 5.1:303-306 -- "an absolute
URL, a bundle-relative path, or a path into a `references/` subdirectory").
The locator is ours, and it has to be: 5.1 has no field for a place within a
resource, and the pinned guard (1.3.0) rejects every route to putting one
inside a `sources` entry -- a non-allowlisted key by name, a nested flow list
as "scalar leaves only", and quoting as an unsupported form. So the locator is
top-level keys shaped like `source_offset`, and a path carrying a flow
terminator is refused fail-fast rather than mangled.

The unit table is built AT EXTRACTION, where the extracted text and the
original's structure are known to agree: pdf -> `source_pages` from
pdfplumber's own page numbers (a page that yielded no text does not renumber
the ones after it), xlsx -> `source_sheet` + `source_rows`, everything else ->
`source_lines`. `source_offset` stays.

Two measurements changed the design before it shipped. A `paragraphs` key for
docx would name a number the document does not have: `<w:p>` counts of
108/27/65/176/57 against converted-markdown lines of 75/33/67/144/63, not one
pair agreeing -- so the key is `source_lines` and says what it indexes. And an
empty spreadsheet row renders exactly like a table separator: the content-based
rule ate 8 empty rows on the K2 price sheet and reported its last row as 92
against a workbook that says 100. The separator is now found by position, and
`tomrad.xlsx` keeps that red.

One profile moves. `provenance` is a policy object, `None` everywhere but
`SEGMENTED_OKF_V0_2`; the other five shipped profiles are byte-identical.

K2 rebuilt from a frozen src copy: 629 concepts, 1108 files, name set identical,
0 ids moved, 479 files byte-identical, 629 changed and 0 lines removed anywhere.
629/629 now carry an address and a locator. New ref
`sha256-tree:665563a2f74423fcbcc8e4f0b0954ee73b73985ac0418de4f6987bd162a1f7c8`;
`2f82fcfe...` is stale. The pre-pass payload does not grow by one byte
(209 092 B before and after, 18 changed lines: the ref and eight per-concept
digests) -- because an excerpt carries the body, not the frontmatter, which is
also why the consumer still cannot cite "file X page 12" from a payload alone.

Report: docs/2026-09-08-proveniens-k2.md. 1339 tests, ruff and mypy clean.

Co-Authored-By: Claude <claude-opus-5>

tests/fixtures/README.md

@@ -17,6 +17,7 @@ and reproducible from that one file.
 |---|---|
 | `two-line-krav.pdf` | One heading plus one requirement row with label and value on the **same line**. That pairing is the property `pdfplumber` was chosen for. |
 | `no-text-layer.pdf` | A structurally valid page with no text operators — the shape a scanned or image-only PDF presents. Must fail fast (`extractor_empty_pdf`), never persist as an empty concept. |
+| `three-page-krav.pdf` | Three pages, one line of text each, and **the middle page carries no text operators**. The extractor drops empty pages, so the last page's text belongs to page 3 — which is what separates a page NUMBER from a count of the pages that produced text. Two pages could not tell those apart. |
 
 ## The office fixtures
 
@@ -35,6 +36,7 @@ symmetric — which is most of them.
 | `two-line-krav.docx` | A heading plus one requirement row with label and value on the **same line** — the docx mirror of `two-line-krav.pdf`. |
 | `no-styles-krav.docx` | The **same document without `word/styles.xml`**. A negative control: the body survives and the heading marker does not, which is what proves the styles part is load-bearing rather than decoration. |
 | `two-line-krav.xlsx` | A sheet name that becomes a heading, plus a label/value pair on one row. |
+| `tomrad.xlsx` | Four rows with the **third one empty**. The converter renders an empty row as a pipe line of nothing but spaces, which is what a pipe table's own separator line also looks like — so a rule that reads the line rather than its position swallows the row and renumbers every row after it. Found on the K2 price sheet (8 empty rows, last row reported as 92 against a workbook that says 100); this fixture is what keeps it red. |
 
 Two things were measured while building these, and both are the same shape —
 structurally valid input, silently reduced output, exit code 0 and no warning: