fix: emit block line numbers when with_meta is set (#291)

[livingstaccato]

Fixes #291.

What

SerializationOptions.with_meta produced no metadata. The option, the hcl2tojson --with-meta flag and the v8 migration guide's promise that the v7 keys are "still available" all survived the rewrite; the code that emitted them did not. v7 wrote the keys from RuleTransformer.block, and v8 moved block serialization into BlockRule.serialize without carrying them over, so the option was read nowhere in the package.

BlockRule.serialize now emits __start_line__ and __end_line__ alongside the body -- the same innermost dict the labels nest around, which is where v7 put them. The line numbers in the tests were checked against python-hcl2 7.3.1 on the same input, so they are v7's values rather than merely self-consistent.

A tree built by the deserializer carries an empty Meta, so it reports no keys rather than inventing zeros.

Also here

• BlockView.start_line / .end_line, so a span can be read from the query API without serializing the block. with_meta puts the numbers in the output dict, which otherwise meant reaching them through the label nesting or through the rule's private _meta. Both are None for a deserialized tree. hq picks them up through its property accessors: hq 'resource[*] | .start_line' main.tf.
• Tests pinning what happens to an attribute genuinely named like a metadata key. The keys travel in-band, so dumps(loads(...)) drops such an attribute and with_meta overwrites it -- as already happened for __is_block__ and __comments__ before these two keys existed. That collision is filed separately as __is_block__, __comments__ and the with_meta keys silently displace attributes of the same name #331, and this PR makes it worse rather than merely inheriting it: before, __start_line__ was an ordinary attribute that survived a round trip, and after, it does not -- on the default path, with with_meta off. The tests state that rather than defend it. __is_block__, __comments__ and the with_meta keys silently displace attributes of the same name #331 now has an out-of-band fix in progress, which is where the collision goes away for all five names; if that lands first this PR should rebase onto it instead of reserving the two names in-band.

Note for merge order

This branch and the one for #328 both touch hcl2/query/blocks.py on adjacent lines. Whichever lands second will want a keep-both resolution.

Merging

It touches the same code as #332 (hcl2/query/blocks.py), #345 (hcl2/deserializer.py and hcl2/rules/base.py). Whichever of those lands first, this one needs a rebase rather than a merge — the overlaps are real edits to the same methods, not adjacent lines, so resolving them by hand risks losing one of the two fixes. Say the word and I will rebase and re-run the suite.

---

This pull request, and the investigation behind it, were produced by an AI assistant (Claude) working on behalf of the author. Please review with that provenance in mind.

[livingstaccato]

Please hold off on merging this one for now — I want to do another review pass over it before it goes in. Opened as a draft for that reason; I will mark it ready and say so here once I am done.

[livingstaccato]

Review pass done, so the hold above no longer applies — this is ready for review now.

Rebased on current main; GitHub reports it mergeable as it stands.

_{🤖 Drafted with Claude Code.}

[livingstaccato]

Brought up to date with current main (0f74596) — GitHub had this flagged as
conflicting, which was only CHANGELOG.md and the merge=union driver that the
web UI does not honour. This one conflicts with #332 and #345 (hcl2/query/blocks.py,
hcl2/rules/base.py) rather than with main.

Merge order. Eight of the twelve open PRs apply to main in sequence with no
conflict at all — verified by merging each and running the suite, not by
inspection:

#332 → #334 → #335 → #345 → #346 → #349 → #352 → #354

(1552 → 1563 → 1591 → 1627 → 1671 → 1696 → 1703 → 1711 passing, from a 1534
baseline; each adds its own tests.) The other four — #333, #348, #350, #351 —
conflict with siblings rather than with main, so no ordering avoids them.

A resolved integration of all twelve is on the fork if it is useful:
livingstaccato/python-hcl2:int/pyvider-hcl-9 — 1784 passing, ruff and mypy
clean. Not proposed as a PR; the twelve are more reviewable apart.

_{Drafted with the help of an LLM, working on behalf of the author.}