fix: read archived session usage without source sync

[shunkakinoki]

Request agentsview session usage --no-sync when collecting usage so background cost lookups read the archive without requesting source synchronization. Full subagent attribution remains enabled, and missing sessions or absent token/cost data still return no usage for existing retry handling.

This requires a released AgentsView CLI with session usage --no-sync support. Unsupported CLIs report the provider error; the legacy token-use fallback is removed because it cannot guarantee the no-sync contract. The configured HTTP endpoint path is unchanged. Keep this draft pending the companion AgentsView change and a release containing it.

T3 thread

[roborev-ci]

roborev: Combined Review (ec247cd)

Verdict: Changes require fixes for 1 finding.

Medium

• internal/tokens/tokens.go:220: --no-sync is passed unconditionally, so AgentsView versions that support session usage but not this flag return an error instead of providing token counts, contradicting documented older-version support. On an unsupported-flag error, fall back to the prior compatible usage command and legacy token-use path where needed, or remove older-version support and update the affected documentation.

  Reported by: codex

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Reviewers: 2 done | Synthesis: codex, 6s | Total: 1m48s