GitHub transport: whole-map GraphQL read and single-ticket REST refresh

[mayfieldiv]

Implements part of the wayfinder ticket surface. Read first: the spec — the resolution comment on #112 — and CONTEXT.md's ### Wayfinder tickets section (on main, merged via PR #113), plus AGENTS.md. Use the spec's vocabulary exactly.

Spec §4; full API evidence on local branch research/github-subissues-dependencies (docs/research/github-subissues-dependencies.md).

• Wire types (Issue, IssueState, SubIssuesSummary, DependenciesSummary) in src/github/types.rs after IssueComment — permissive #[serde(default)] posture.
• fetch_wayfinder_map in src/github/graphql.rs (query verbatim from spec §4.1; envelope must impl GraphQlErrors), modelled on fetch_review_status/fetch_review_threads.
• get_issue + list_issues_with_label in src/github/rest.rs beside list_issue_comments; get_all accepts only per_page — generalize or pre-bake the query string.
• Blocked-ness inputs come from the blockedBy list filtered on state == OPEN — never the eventually-consistent summary counter. Keep each node's repository.nameWithOwner (External Dependency detection).
• Never call GET …/parent; treat every 404 as a genuine error (it is — including the missing-Issues-scope case).
• Fallback detection only (spec §4.4): a map with zero sub-issues but a task-list body, or Part of #n/Blocked by: #n leading lines, yields a "degraded dialect" signal for the effort card — no body-line parsing into the model.
• Parsers as pure parse_* functions with fixture tests in graphql/tests.rs / rest/tests.rs.

[mayfieldiv]

Resolution: implemented spec §4 as pure transport + normalization, merged via PR #126 (rebase; commits 786055c + 0c2c187).

• fetch_wayfinder_map (graphql.rs) runs the spec's verbatim one-query map read; the envelope impl GraphQlErrors with a test proving HTTP-200 errors can't parse as empty success. Normalizes straight into ticket::Effort; blocked-ness inputs come from the blockedBy list with per-node state + repository.nameWithOwner — the summary counters aren't deserialized on this path at all.
• get_issue / list_issues_with_label (rest.rs) via a generalized get_all_with; GET …/parent is never called and every 404 stays a genuine error; the listing drops PRs (pull_request marker).
• §4.4 detect-and-degrade only: fallback_dialect on zero-sub-issue task-list maps; has_fallback_dependency_lines for ticket bodies (leading lines, stops at the first ##, requires an issue ref). Nothing parsed into the model.
• Per-Effort degradation (§5.5): a malformed map lands in failed_maps (map number + error) instead of discarding the repo's other Efforts.
• Wire types Issue/IssueState/SubIssuesSummary/DependenciesSummary in types.rs; shared claim_from_assignees / ticket_type_from_labels so Fetch integration: efforts and tickets through the runtime #120's refresh path can't drift from the map read.

Small decisions the spec didn't settle, resolved here:

• A same-repo blocker that isn't one of the map's sub-issues is an External Dependency, not Unknown — its state/title were captured, so "can't find or read" would be false. Same-effort membership means "sub-issue of this map", not "same repo".
• Ticket URLs aren't stored: they derive from TicketKey (the PrKey::html_url() precedent); Ticket detail page #122 adds the /issues/ accessor.
• parent_issue_url stays a raw wire string until a consumer navigates by it (then it parses into an EffortKey).
• Assignees on closed tickets are kept — state × claim are orthogonal axes (spec §1); GitHub's Claim is the first assignee when several exist.
• A truncated blockedBy page (impossible under first:50) degrades to an Unknown Dependency ("additional blockers") so unseen blockers can't put a ticket on the Frontier; >10 open maps or >100 sub-issues log a warning rather than truncate silently.

Notes for later tickets: #118 should lift destination_from_map_body / body_has_task_list out of graphql.rs into a shared dialect module (the local map.md parser needs the same extraction); "fallback dialect" is spec-§4.4 vocabulary with no CONTEXT.md glossary entry yet — worth adding when #120/#121 render the degradation notice.