events: add performance MSRs to boot event

[ripatel-fd]

Collect x86 model-specific registers on startup and report them
back to telemetry. It turns out some hardware mitigations like
BpSpecReduce get enabled even if mitigations are off and cause a
big performance impact (e.g. through SEV-SNP).

[github-actions]

 ┌─ ⚡ PERF · 018b4cb vs main@2fc40e5 ─────────────────────────────────
 │ SUITE                               BASELINE          NEW         Δ
 │ replay tps, mainnet               28,305 tps   28,232 tps  ·  -0.26%
 │ bench tps, localnet              128,647 tps  128,646 tps  ·   0.00%
 │ snapshot load, testnet               15.66 s      15.77 s  ·  +0.72%
 │ mem total, mainnet                171.44 GiB   171.44 GiB  ·   0.00%
 │ mem total, testnet                102.31 GiB   102.31 GiB  ·   0.00%
 │ clean compile, firedancer        315.9 cpu·s  320.4 cpu·s  ·  +1.44%
 │ binary size, firedancer             85.94 MB     85.95 MB  ·  +0.01%
 ├─────────────────────────────────────────────────────────────────────
@@ 0 REGRESSIONS · 0 WARNINGS · 0 IMPROVED · 7 NOISE @@
 └─────────────────────────────────────────────────────────────────────

[Copilot]

🟡 Changes recommended

Moderate findings remain unresolved around EINTR handling, optional-field test support, and nested nullable-type validation.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds CPU0 x86 MSR collection to boot telemetry for diagnosing hardware mitigation performance effects.

Changes:

• Adds seven optional MSR fields to event schemas.
• Collects and publishes available MSR values with presence tracking.
• Extends nullable integer schema generation.

File summaries

File	Reviewed changes and final findings
src/disco/events/schema/events.proto	Adds optional MSR fields. Moderate (2 votes): update the test parser for optional and add presence/value assertions.
src/disco/events/schema/boot.json	Defines nullable MSR telemetry columns.
src/disco/events/gen_events.py	Adds nullable integer generation. Moderate (2 votes): reject or recursively validate nullable types nested in tuples or arrays.
src/disco/events/fd_boot_report.h	Stores MSR values and presence flags.
src/disco/events/fd_boot_report.c	Reads and publishes MSRs. Moderate (2 votes): retry pread on EINTR. Moderate (1 vote): update the boot-report decoder and test successful MSR publication.

Review details

Suppressed comments (1)

src/disco/events/fd_boot_report.c:326

• The existing test_boot_report decoder only strips repeated, so it does not recognize these new optional declarations. On a host where /dev/cpu/0/msr is readable, at least msr_x86_spec_ctrl is emitted, the declaration is skipped by proto_msg_fields, and check_msg fails on the unknown field; update the test parser and cover the presence/value path.

  r->msr_x86_spec_ctrl_present = !read_msr( 0U, 0x00000048UL, &r->msr_x86_spec_ctrl );
  if( r->cpu_vendor==2 ) { /* AMD specific */

• Files reviewed: 5/5 changed files
• Comments generated: 3
• Review effort level: Lite

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