[nicolas-abril]

Three runtime simplifications in bend2/comp.ts (65,994 → 65,977 ttok). Each removes something nothing uses or a case the general path already covers.

• JS io_sys no longer binds pread. Its only user was the old effs/file_read.js, which moved to fs.readvSync in fix(io): File.read and its twins read through fs on Node, where bun:ffi is missing #1881. No effect, test, demo or the CLI calls it. read stays: guide/EFFECTS.md documents it as part of io_sys() for user effects. file_read_no_ffi.bend's comment now says io_sys binds read and once bound pread.
• ALC[CUBE_T + 1] becomes ALC[CUBE_T]. The extra row was for the old ALC[1 + arg] indexing. Since The host's column grows to a LINE of tasks a thread again, a drain splits its rows into units of 32 a thread, and rings rewind between turns (stacked on #1092) #1269 the main thread uses ALC[0] and the pool workers use ALC[1 .. pool_size - 1], and pool_size <= CUBE_T. The unused 768-byte row goes.
• io_park_add sets w->prev = w->next->prev. The w->next == w ? w : … case is redundant: when w is the only parked node, the next line, w->next->prev = w, writes the same field.

Verified (on main b5e6b2e)

• Emitted output: stdout, stderr and exit codes match main for every .bend under tests/, demos/ and bench/runtime/ (1,923 files, C and JS). The only differences in the emitted text are these three lines.
• Clang: all 930 emitted C programs compile cleanly under clang's unused-function and unused-macro warnings, and the 67 ! programs under Metal. No runtime function or macro goes unused, apart from CUDA-, Linux- and ObjC-only code, which I checked by hand.
• tsc: comp.ts type-checks with the same errors as main.
• Gates: repo 56/56, test 1838/1838, perf level with main run back to back (121 vs 120 / 124; the machine is noisy).

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