tri hot: every hot-reload speed-up as one word -- watch, frontier, prebuild, suite, caches #8952

Part of #8737 (hot reload), epic #8095. The owner asked for every speed-up to be in the tri CLI.

Problem

Each speed-up of the overnight loop sits behind a different t27c subcommand and flag. Nothing in tri reaches them except the timing check tri hot (#8872), so using them means remembering:

• t27c frontier --watch;
• t27c frontier --list;
• t27c silicon ... --skip-hardware to warm the bitstream cache without the cable;
• t27c suite --fast --corpus-only;
• where the caches live, and their eviction limits.

Change

tri hot <action>, with the command strings in specs/tri/hot/hot.t27:

Acceptance criteria

• tri hot --help names every action.
• On this Mac:
  • tri hot reads OK on both paths;
  • tri hot caches prints the three caches with their limits;
  • tri hot frontier prints the frontier summary;
  • tri hot prebuild specs/fpga/ternary_link.t27 --top fpga/verilog/ternary_link_jtag.v --pnr-seed 11 reads bitstream REUSED;
  • tri hot watch starts the watch.
• Hand-written foreign lines do not grow.

Boundary

specs/tri/hot/hot.t27

User Scenarios

• Given the tri CLI is installed, when a developer runs tri hot --help, then the output lists all six actions: check, watch, frontier, prebuild, suite, and caches.
• Given a Mac with the repository checked out, when a developer runs tri hot caches, then the command prints the three caches (frontier, bitstream, corpus) with their entry counts and eviction limits.
• Given a spec file and its top-level output, when a developer runs tri hot prebuild specs/fpga/ternary_link.t27 --top fpga/verilog/ternary_link_jtag.v --pnr-seed 11, then the output contains bitstream REUSED indicating the bitstream cache was warmed without hardware.

Requirements

FR-001: The tri hot command MUST accept a subcommand action with values check, watch, frontier, prebuild, suite, caches, defaulting to check.
FR-002: tri hot check MUST execute the timing check from issue #8872, validating warm frontier and reuse hit budgets.
FR-003: tri hot watch MUST invoke t27c frontier --watch to enable save-triggered incremental rebuilds at ~3% idle CPU.
FR-004: tri hot frontier MUST invoke t27c frontier --list and print the reuse frontier summary.
FR-005: tri hot prebuild <spec> --top <v> [--pnr-seed N] MUST invoke t27c silicon ... --skip-hardware to warm the bitstream reuse cache for the given spec and top module without touching hardware.
FR-006: tri hot suite MUST invoke t27c suite --repo-root . --fast --corpus-only to run all per-spec phases in parallel.
FR-007: tri hot caches MUST read ~/.cache/t27 and print each cache's entries and size against its eviction limit, using data from generated code of gen_hash_cache.t27 and bitstream_reuse.t27.
FR-008: All command strings for the above actions MUST be defined in specs/tri/hot/hot.t27.
FR-009: Hand-written foreign (non-t27) lines in the codebase MUST NOT increase as a result of this change.