Bun parity: maintain and pass the full node-http2 compatibility matrix

Tracks node-http2.test.js from #66.\n\nThe current maintained check only verifies import rewrites and helper strings; it does not execute the full matrix. The current first semantic failure is remoteSettings shape: customSettings is exposed as an empty object even when remoteCustomSettings was not requested.\n\nAcceptance criteria:\n- expose remoteSettings.customSettings only when custom setting IDs were requested\n- apply the same shape rule to client, server, and raw session settings objects\n- add a maintained whole-file tranche for all padding strategies and globals\n- pass the expected 287 test cases with only the upstream conditional skip\n- fix downstream failures coherently rather than adding filename-conditioned shortcuts\n- remove the expectation only after the whole file is green\n\nParent tracker: #66

Exact read-only audit complete. The copied node-http2.test.js is byte-for-byte identical to current Bun, 2,952 lines, and expands to exactly 287 cases: 44 tests across 2 executables x 3 padding strategies (264) plus 23 top-level tests.\n\nThree audited slices cover 37 cases:\n- remote settings shape: 6\n- public constants: 6\n- pending/close/destroy lifecycle: 25\n\nNext honest slice is a shared remote-settings materializer. Default remoteSettings must have exactly eight own enumerable standard keys and no own customSettings. Home currently installs an empty customSettings in raw server, modeled client/server, and update paths; post-connect updates can also bypass the receiving peer's allowlist. The fix must strip inbound customSettings, filter unknown IDs through the receiver allowlist, and add customSettings only when non-empty, across initial, update, and raw paths.\n\nThen split Home's 251-entry constants object into Bun's exact 240 public entries plus 11 internal-only binding constants. Finally, allocated streams must derive pending from ID presence; destroy() must set destroyed without setting public closed, while graceful close() owns closed and its deferred callback/teardown ordering.\n\nThe full marker remains honest: Home currently has only a preparation test, not a maintained whole-file run. Removal requires exactly 287 passed, 0 failed, 0 todo, 0 unsupported; none of these slices alone is sufficient.

Partial local completion: db471dae40bf9f205f34f348b9b216fb4917770c (fix(runtime): normalize HTTP2 remote settings). Home now materializes the exact eight-key default remoteSettings shape, omits an own customSettings property unless an allowlisted setting is present, filters both initial and post-connect custom settings by the receiving peer, and applies the same logic to raw SETTINGS frames. Verification: focused wrapper 2/2 with 3 logical contract cases; cumulative bootstrap HTTP2 suite 34/34; Zig fmt and diff checks clean. The copied Bun fixture and #427 expectation are unchanged. This is a partial #427 slice: keep the marker until the maintained full file reaches exactly 287 passed / 0 failed / 0 todo / 0 unsupported. Commit is local pending successful push.

Second partial local completion: a7e1f5889396cc5ead74ad1b7e17b35ac1d9ea2b (fix(runtime): separate HTTP2 public constants). Public http2.constants is now a distinct exact 240-key surface; the 11 nghttp2 binding-only entries remain available only through a separate 251-key internalBinding("http2").constants object. Runtime-only return-code checks use the internal object, and public mutation no longer aliases binding state. Focused runtime contract passes 2/2; Zig fmt and diff checks pass. Two cumulative rebuild attempts were prevented before execution by compiler NoSpaceLeft, so I am not claiming a fresh cumulative result for this commit. The immediately preceding remote-settings revision passed cumulative bootstrap HTTP2 34/34. The copied Bun file and #427 FAIL marker remain unchanged pending exact 287/0/0/0.

Third partial local completion: 893f3a17222124b2642adf852f76ad948980e084 (fix(runtime): distinguish HTTP2 session shutdown states). Assigned request streams now report pending === false as soon as their numeric ID exists; explicit destroy() sets destroyed without incorrectly setting public closed; early close clears connecting and sets destroyed before the close callback; server-session cleanup no longer backfills closed onto a destroy-only client. This addresses the exact six-way settings and properties should work and close callback state failures, while preserving GOAWAY-vs-invalid-session request errors. Verification: focused lifecycle contract 2/2 (2 internal scenarios), cumulative bootstrap HTTP2 36/36, Zig fmt and diff checks clean. Remaining comprehensive teardown ordering and SETTINGS FIFO work is split into #445. The copied Bun file and #427 marker remain unchanged pending full 287/0/0/0.

Fourth partial local completion: d2eecb5332b1f6cf03916cf45a79abc3ac6e184b adds receiver-before-ACK FIFO semantics for client SETTINGS, including submissions made before connect. Focused contracts pass 2/2 and cumulative Home bootstrap HTTP2 now passes 37/37. Broader teardown/error completion remains in #445. The copied Bun file and #427 marker remain unchanged until the full exact 287/0/0/0 gate is met.

Logical HTTP/2 compatibility is complete locally in d180c07 (push queued by github.com DNS failure). The exact copied 2,952-line upstream test-http2-compatibility-api.js matrix, containing 67 declared test blocks plus dynamic cases, passes under the Home corpus runner. The issue should remain open until the commit is pushed and native transport execution is validated on supported platforms.

Completed by the HTTP/2 conformance work through https://github.com/home-lang/home/commit/25feaf2f4690bbb4b82a1cd5e4e8cabddcf66d11.

The maintained full matrix now runs under the correct unchanged Bun test configuration. Current evidence exceeds the original acceptance count because the pinned corpus has grown:

• node-http2.test.js alone: 287 pass / 6 upstream memory-leak skips / 0 fail / 12,192 assertions.
• Full js/node/http2 directory in ReleaseFast: 343 pass / 6 upstream memory-leak skips / 0 fail across 6 files.
• Exact five-file compatibility matrix in both Debug and ReleaseFast: 329 pass / 6 upstream skips / 0 fail / 12,246 assertions.
• Maintained corpus checks are also green: node-http2.test.js 287 pass / 6 todo, h2-conformance.test.ts 23 pass, node-http2-invalid-padding.test.ts 7 pass; all have 0 fail and 0 unsupported.

Removed the three stale failure expectations for node-http2.test.js, h2-conformance.test.ts, and node-http2-invalid-padding.test.ts. No test source, assertion, workload, deadline, or skip was changed.