Keep one draft per source, not per directory

CHANGELOG.md

@@ -5,14 +5,15 @@
 - Converting a document is now `in2lambda convert FILE FILTER`, with the same options as before (`-o/--out`, `-a/--answers`). Scripts and Docker invocations that run `in2lambda FILE FILTER` need the extra word.
 - `in2lambda FILE FILTER` exits with an error naming the command to run instead, rather than printing its usage and exiting successfully.
 - beartype is now `^0.22`. At 0.20.0 and below its import hook leaves `cli` a plain function rather than a group, so the new command line either fails to import or runs `convert` whatever the arguments; 0.20.1 is the first version that works.
-- `in2lambda source add FILE` freezes a document: it converts .docx and .tex to markdown beside the file, and writes a `draft.json` holding the markdown's hash and every block in it with the lines it spans, so that another tool can quote the source by line range. `in2lambda source show` prints that markdown numbered with the block ids. Freezing a file that has changed since is refused unless `--start-over` says to discard the draft, and so is showing one, since its block ids would name lines they are not the ids of. Both need pandoc and the `convert` extra, as `convert` does.
-- A draft now holds a `log` of every command that changed it and a `fields` map of what those commands wrote, each field recording which layer wrote it (1 a spec, 2 a predicate, 3 a line range, 4 a literal), the source ranges it was copied from, whether it has been edited and by whom. `in2lambda draft mark ignore BLOCK` is the first such command, and `in2lambda draft replay` rebuilds the draft from the frozen markdown and the log, refusing unless what it builds is the `draft.json` that is there, byte for byte. A `draft.json` written before this has no `log` in it and is refused as one nothing here wrote; `in2lambda source add --start-over` freezes the document again.
+- `in2lambda source add FILE` freezes a document: it converts .docx and .tex to markdown beside the file, and writes a `FILE.draft.json` beside it, holding the markdown's hash and every block in it with the lines it spans, so that another tool can quote the source by line range. The draft is named after the source, so a folder holding a term's worth of sheets holds a draft for each. `in2lambda source show` prints that markdown numbered with the block ids. Freezing a file that has changed since is refused unless `--start-over` says to discard the draft, and so is showing one, since its block ids would name lines they are not the ids of. Both need pandoc and the `convert` extra, as `convert` does.
+- A draft now holds a `log` of every command that changed it and a `fields` map of what those commands wrote, each field recording which layer wrote it (1 a spec, 2 a predicate, 3 a line range, 4 a literal), the source ranges it was copied from, whether it has been edited and by whom. `in2lambda draft mark ignore BLOCK` is the first such command, and `in2lambda draft replay` rebuilds the draft from the frozen markdown and the log, refusing unless what it builds is the draft that is there, byte for byte. A draft written before this has no `log` in it and is refused as one nothing here wrote; `in2lambda source add --start-over` freezes the document again.
 - A draft is filled in by `in2lambda draft question add`, `in2lambda draft part add QUESTION` and `in2lambda draft question solution QUESTION`. Each takes `--text` to copy the wording out of the frozen source, as a block id such as `b3` or as lines such as `s10:14`, or `--literal TEXT` where the source does not say it in a form the field can take, which records the field as edited and written by layer 4 rather than 3. Question and part numbers are worked out from the fields already written rather than given, so a replay arrives at the same ids. `in2lambda draft split block BLOCK AT` cuts a block the parser made one of two things into `b3a` and `b3b`, so that each half can be quoted on its own. A command writing a field that is already written, or quoting lines another field was taken from, is refused naming both fields.
 - `in2lambda draft field replace FIELD OLD NEW` changes the wording inside a field that is already written, for the faults only an edit can fix - a brace the OCR dropped out of some maths, which no range of the source says correctly. OLD has to occur in the field exactly once, or the command is refused saying how many times it occurs; `--regex` reads it as a regular expression and NEW as what to replace it with. The field is left quoting the lines it was taken from, at the layer that wrote it, but recorded as edited and by whoever replaced the wording, so the change can be shown against the source.
 - `in2lambda spec run SPEC` runs a YAML file of selectors over the frozen source: it says which blocks are questions, parts and solutions, which to ignore, what to strip off the front of each one, and which of the four filters lays the solutions out. It fills in the draft's fields with the markdown of the lines each was taken from, records the spec's name and hash in the log so a replay runs the same file, and reports every block it made nothing of. Running an edited spec over a draft it has already filled in is refused, as freezing a document that has changed is: `in2lambda source add --start-over` begins the draft again. Reading a spec needs pyyaml, which the `convert` extra now installs alongside panflute. See [the spec page](https://lambda-feedback.github.io/in2lambda/spec.html) for the selectors and layouts.
 - A field quoted out of a list item is now dedented as commonmark reads the item: the marker comes off the first line and as much of the same width off every line under it. So a question written `1.  ` no longer carries its number, a continuation line no longer arrives indented far enough to be rendered as a code block, and a spec's `strip` is left with what pandoc does not read as a marker. Values written by `in2lambda spec run`, `in2lambda draft question add`, `in2lambda draft part add` and `in2lambda draft question solution` change accordingly; the ranges behind them still name the same source lines.
 - `in2lambda validate` checks a draft over as a whole and writes what it finds into it as a `report`: source blocks in no field and not marked ignore, two fields taken from the same lines, gaps in the numbering of the questions or their parts, and fields holding nothing, each at level `error`; a part, or a question written without parts, that nothing in the draft answers is reported at level `warning` instead. Each finding names the level, the field and the lines it is about, so it can be acted on without reading the draft. Finding something is not a failure and the command still exits 0; the report is replaced by the next run of the checks and dropped by the next command that changes the draft, since it describes the draft as it stood. It also checks over the set the draft describes, as a converted document is checked at export - maths delimiters, what KaTeX will not render, images the export would not carry, and the compile Lambda Feedback's PDF generator does where pandoc and xelatex are installed, with a warning saying what to install where they are not - and reports each of those against the draft field the text is written in, at level `error`, so that `in2lambda build` refuses them as it refuses anything else at that level.
-- `in2lambda build` writes the draft in this directory out as a Lambda Feedback set: one question per `qN.text` field, holding the parts written for it and the worked solutions, with the images those fields refer to under `media/`, as `in2lambda convert` writes a set - a field naming an image that is not beside the draft is refused saying which file is missing, since the checks read the draft and not the folder it is in, and a question's own solution written beside a solution for every part it has becomes a part of its own holding just that solution, as `convert` pairs them up. It is refused unless `in2lambda validate` has been run since the draft last changed - every command that changes one drops its report - and found nothing at level `error`, and the refusal prints those findings so they can be acted on without opening the draft. A finding at level `warning` - a part or question nothing in the draft answers - does not stop it: half the sheets there are keep their solutions in another file or have none at all, so the warning is printed and the set written all the same, rather than a solution having to be invented to quiet it. `in2lambda render` writes each question as a PDF instead, compiled as Lambda Feedback's own PDF generator compiles it, which needs pandoc and xelatex; it is gated on nothing, since looking at a draft is how what the checks found gets fixed. Both take `-o/--out`, as `convert` does.
+- `in2lambda build` writes a draft out as a Lambda Feedback set: one question per `qN.text` field, holding the parts written for it and the worked solutions, with the images those fields refer to under `media/`, as `in2lambda convert` writes a set - a field naming an image that is not beside the draft is refused saying which file is missing, since the checks read the draft and not the folder it is in, and a question's own solution written beside a solution for every part it has becomes a part of its own holding just that solution, as `convert` pairs them up. It is refused unless `in2lambda validate` has been run since the draft last changed - every command that changes one drops its report - and found nothing at level `error`, and the refusal prints those findings so they can be acted on without opening the draft. A finding at level `warning` - a part or question nothing in the draft answers - does not stop it: half the sheets there are keep their solutions in another file or have none at all, so the warning is printed and the set written all the same, rather than a solution having to be invented to quiet it. `in2lambda render` writes each question as a PDF instead, compiled as Lambda Feedback's own PDF generator compiles it, which needs pandoc and xelatex; it is gated on nothing, since looking at a draft is how what the checks found gets fixed. Both take `-o/--out`, as `convert` does.
 - An export now names its images as they sit in `media/`: every markdown image reference a question holds - in its text, a part's, a worked solution, a final answer or an answer box's wording - is rewritten to the file name the image was carried under, so a document writing `![](figures/train.png)` exports as `![](train.png)` beside `media/train.png` and Lambda Feedback finds the figure where it looks for one. A file two questions use is carried once; where two different files are called the same, the second is named as Lambda Feedback's own exports name an image, `question_001_<Title>_0001.png`. Reading an export back is unchanged, since an export already names its images this way.
+- Every command that works on a draft - `in2lambda source show`, each of the `in2lambda draft` commands, `in2lambda spec run`, `in2lambda validate`, `in2lambda build` and `in2lambda render` - takes `--draft`, naming either the draft or the source it was frozen from. Left off, it uses the one draft in the current directory, and where there is more than one it is refused naming them rather than acting on whichever sorts first. `in2lambda spec run` names its SPEC from the draft's directory. The Python functions behind them take the draft's path rather than a directory: `in2lambda.source.frozen`, `in2lambda.source.show`, `in2lambda.draft.execute`, `in2lambda.draft.replay`, `in2lambda.draft.spec_command`, `in2lambda.draft.report.validate`, `in2lambda.draft.export.build` and `in2lambda.draft.export.render`. `in2lambda.source.draft_of` says where a document's draft goes and `in2lambda.source.find` is what the command line resolves `--draft` with.
 - Importing `in2lambda.katex_convert` no longer writes a file called `log` into the working directory. What it has to say about a converted expression goes to the `in2lambda.katex_convert` logger, which is silent unless the application configures logging.
 - The Python API is unchanged: `in2lambda.main.runner` and everything under `in2lambda.api` take the same arguments and return the same objects.